Amphiboles and Other Hydrous Pyriboles - Mineralogy 093995009X, 0939950103
241 47 162MB
English Pages 372 [384] Year 1981
Polecaj historie
Table of contents :
Page 1
Titles
REVIEWS In
MINERALOGY
Volume 9A
DAVI D R. VEBLEN, Editor
The Authors
Subrata Ghose
Malcolm Ross
James B. Thompson, Jr.
David R. Veblen
Tibor Zoltai
Series Editor
Paul H. Ribbe
MINERALOGICAL SOCIETY OF AMERICA
Page 1
Titles
COPYRIGHT
Mineralogical Society of America
PRINTED BY
REVIEWS IN MINERALOGY
ADDITIONAL COPIES
ii
Tables
Table 1
Table 2
Page 1
Titles
AMPHIBOLES and Other
TABLE of CONTENTS Page
CHAPTER 1. CRYSTAL CHEMISTRY OF THE AMPHIBOLES Frank C. Hawthorne
Tables
Table 1
Page 2
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........................
Tables
Table 1
Page 3
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CHAPTER 2. AMPHIBOLE SPECTROSCOPY
Frank C. Hawthorne
Page 4
Titles
CHAPTER 3. AN INTRODUCTION TO THE MINERALOGY AND PETROLOGY
OF THE BIOPYRIBOLES James B. Thompson, Jr.
CHAPTER 4. NON-CLASSICAL PYRIBOLES AND POLYSOMATIC REACTIONS
IN BIOPYRIBOLES David R. Veblen
Page 5
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CHAPTER 5. AMPHIBOLE ASBESTOS MINERALOGY
Tibor Zoltai
Page 6
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CHAPTER 6. THE GEOLOGIC OCCURRENCES AND HEALTH HAZARDS
OF AMPHIBOLE AND SERPENTINE ASBESTOS Malcolm Ross
Page 7
Titles
CHAPTER 7. SUBSOLIDUS REACTIONS AND MICROSTRUCTURES
IN AMPHIBOLES Subrata Ghose
For contents of Volume 9B, "AlfPHIBOLES: Petrology and Experimental
xii
Page 1
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REVIEWS in MINERALOGY
FOREWORD
iii
REV009Apreface.pdf
Page 1
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PREFACE and ACKNOWLEDGMENTS
Page 2
Page 1
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Chapter 1
CRYSTAL CHEMISTRY of the AMPHIBOLES
Page 2
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- Si per formula unit-
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Figure 2 appears on the facing page.
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4
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Chapter 3
An INTRODUCTION to the MINERALOGY and PETROLOGY of the BIOPYRIBOLES
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MacLeod, W.N. (1966) The Geology and Iron Deposits of the Hamers Leu Range Area, Western
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Chapter 7
SUBSOLIDUS REACTIONS and MICROSTRUCTURES in AMPHIBOLES
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Citation preview
REVIEWS In MINERALOGY Volume 9A
AMPHIBOLES and OTHER HYDROUS PYRIBOLES - MINERALOGY DAVI D R. VEBLEN, Editor The Authors Subrata
Ghose
James B. Thompson,
Dept. of Geological Sciences University of Washington Seattle, WA 98195
Frank
C. Hawthorne
David R. Veblen
Dept. of Earth Sciences University of Manitoba Winnipeg, Manitoba R3T 2N2 Canada
Malcolm
Ross
Jr.
Dept. of Geological Sciences Harvard University Cambridge, MA 02138
Dept. of Earth and Planetary Sciences The Johns Hopkins University Baltimore, MD 21218
Tibor Zoltai
U.S. Geological Survey 959 National Center Reston, VA 22092
Series Editor
Dept. of Geology and Geophysics University of Minnesota Minneapolis, MN 55455
Paul H. Ribbe Department of Geological Sciences Virginia Polytechnic Institute and State University Blacksburg, Virginia 24061
MINERALOGICAL
SOCIETY
OF AMERICA
COPYRIGHT 1981 Mineralogical Society of America PRINTED BY BookCrafters, Inc. Chelsea, Michigan 48118
REVIEWS (Formerly:
IN MINERALOGY SHORT COURSE NOTES)
ISSN 0275-0279 VOLUME 9A: AMPHIBOLES and Other Hydrous Pyriboles - Mineralogy ISBN 0-939950-09-X 0-939950-10-3
ADDITIONAL
COPIES
Additional copies of this volume as well as those listed below may be obtained at moderate cost from Mineralogical Society of America 2000 Florida Avenue, NW Washington, D.C. 20009
Vol. 1:
SULFIDE
Vol. 2:
FELDSPAR
MINERALOGY, MINERALOGY,
P.H. Ribbe,
Editor
P.H. Ribbe,
Editor
Vol. 3:
OXIDE MINERALS,
Vol. 4:
MINERALOGY and GEOLOGY of NATURAL F.A. Mumpton, Editor (1977)
Vol. 5:
ORTHOSILICATES,
Vol. 6:
MARINE
Vol.
PYROXENES.
7:
Vol. 8:
MINERALS,
Douglas
Rumble
P.H. Ribbe,
(1976)
502 p. 232 p.
(1980)
Editor
381 p.
(1979)
380 p.
(1980)
525 p.
KINETICS of GEOCHEMICAL PROCESSES, A.C. Lasaga R.J. Kirkpatrick, Editors (1981)
Vol. 9A: AMPHIBOLES and Other Hydrous Pyriboles D.R. Veblen, Editor (1981)
and 391 p.
- Mineralogy,
Vol. 9B: AMPHIBOLES: Petrology and Experimental Phase Relations, D.R. Veblen and P.H. Ribbe, Editors (1981)
ii
1981) ~300 p.
ZEOLITES,
Editor
Editor
284 p.
(1975; revised
III, Editor
Roger G. Burns,
C.T. Prewitt,
(1974)
372 p , ~375 p.
VOLUME 9A
AMPHIBOLES and Other Hydrous Pyriboles-Mineralogy TABLE of CONTENTS Copyright
and Additional
Copies
Page ii
Foreword
iii
Preface and Acknowledgments
iv
CHAPTER 1. CRYSTAL CHEMISTRY OF THE AMPHIBOLES INTRODUCTION CLASSIFICATION
1
AND NOMENCLATURE.
The four principal
amphibole
1
3 3
groups
Fe-Mg-Mn amphiboles Calcic amphiboles Sodic-calcic amphiboles Alkali amphiboles
7 7 7
General considerations THE AMPHIBOLE
Frank C. Hawthorne
9
CRYSTAL STRUCTURES
9
Choice of axes Principal structure types Site nomenclature in amphiboles The C2/m amphibole structure The P2l/m amphibole structure The P2/a amphibole structure The Pnma amphibole structure The Pnmn amphibole structure Amphiboles as layer structures Space group variations in amphiboles
11
THE TETRAHEDRAL
12 13
14 17 18 20 21 22 24
DOUBLE CHAIN
25
The C2/m amphiboles
26 26
Covalent bonding model Bond-valence model
29
The P2l/m amphiboles The P2/a amphiboles The Pnma amphiboles The Pnmn amphiboles Ordering of tetrahedrally-coordinated rHE OCTAHEDRAL The The The The The
34 34 34
36 Al
38
STRIP . .
42
C2/m amphiboles P2l/m amphiboles P2/a amphiboles Pnma amphiboles Pnmn amphiboles
42 50 51 52 56 vi
Page rHE M(4) SITE. . . . ..
........................
The C2/m amphiboles The P2l/m amphiboles The P2/a amphiboles The Pnma amphiboles The Pnmn amphiboles General considerations
56 57 58 58 58 59 59
rHE A-SITE .
63
The The The The The
63 64 64 65 66
C2/m amphiboles P2l/m amphiboles P2/a amphiboles Pnma amphiboles Pnmn amphiboles
rHE 0(3) SITE.
.
:ATION DISTRIBUTIONS IN AMPHIBOLES . . . . . • . . . . . . . . . . . _ Aluminum Ferric iron Titanium Ferrous iron Fe-Mg-Mn amphiboles Calcic amphiboles Sodic-calcic amphiboles Alkali amphiboles Magnesium Manganese Lithium Calcium Sodium Potassium Beryllium Boron Cobalt Nickel Chromium Zinc Germanium 'ACTORSAFFECTING CATION ORDERING IN AMPHIBOLES. . . . . • . . . • . . Structure energy Bond-valence Miscellaneous factors Ionic size Strongly polarizing cations Relief of Si-O-Si bond strain Steric considerations Crystal field stabilization energy General considerations
66 69 71 72 73 73 73 75 75 75 76 77 77 78 78 78 79 79 79 79 79 79 80 80 80 81 81 82 82 82 82 83 84
Page
OXIDATION-DEHYDROXYLATION IN AMPHIBOLES. .
85
HIGH-TEMPERATURE CRYSTAL STRUCTURE STUDIES
86
CELL DIMENSIONS.
91
CONCLUSIONS AND SUGGESTIONS FOR FUTURE WORK.
91
ACKNOWLEDGMENTS ••••.•..••.•
93
TABLE A-I.
94
CRYSTAL STRUCTURE REFINEMENTS OF AMPHIBOLES.
CHAPTER 1 REFERENCES . .
CHAPTER 2. AMPHIBOLE
95
Frank C. Hawthorne
SPECTROSCOPY
INTRODUCTION
103
MOSSBAUER SPECTROSCOPY
103 106 107 107 113 113 115 116
Site-occupancy characterization Amphibole spectra
Fe-Mg-Mn amphiboles Alkali amphiboles Sodic-calcic amphiboles Calcic amphiboles General considerations
VIBRATIONAL SPECTROSCOPY . . The hydroxyl
stretching
117 region
119
ELECTRONIC ABSORPTION SPECTROSCOPY Amphibole
126
spectra
128 128 130 130 132 133
Fe-Mg-Mn amphiboles Calcic amphiboles Sodic-calcic amphiboles Alkali amphiboles Other transition
metals
OTHER TYPES OF SPECTROSCOPIC INVESTIGATION .
135
CONCLUSIONS AND SUGGESTIONS FOR FUTURE WORK.
135
ACKNOWLEDGMENTS ...
136
CHAPTER 2 REFERENCES
137
viii
Page
CHAPTER 3. AN INTRODUCTION TO THE MINERALOGY AND PETROLOGY OF THE BIOPYRIBOLES James B. Thompson, Jr. INTRODUCTION
141
PYRIBOLE POLYSOMES
141
PYRIBOLE POLYTYPES UNIT CELLS AND SPACE GROUPS.
147
POLYSOME STABILITY
151
POLYTYPE STABILITY
156
THE CHEMICAL DESCRIPTION OF COMPLEX MINERALS
158
CONDENSED COMPOSITION SPACES, PYROXENES AND MICAS.
162
CONDENSED AMPHIBOLE SPACE. •
166
CONDENSED BIOPYRIBOLE SPACE.
170
BIOPYRIBOLES AND OTHER ROCK MINERALS
176
SUGGESTIONS FOR FURTHER WORK
184
ACKNOWLEDGMENTS ...
185
CHAPTER 3 REFERENCES
186
CHAPTER 4. NON-CLASSICAL PYRIBOLES AND POLYSOMATIC REACTIONS IN BIOPYRIBOLES David R. Veblen INTRODUCTION
189
BIOPYRIBOLE NOMENCLATURE
190
ORDERED NON-CLASSICAL BIOPYRIBOLES
191
Pyribole structures, unit cells, and symmetries Crystal-chemical details of ordered non-classical
Polyhedral Structural
pyriboles
geometries control of chemistry
Electron microscopic biopyriboles
observations
of ordered
wide-chain
Known structure types observed with HRTEM New pyribole structure types discovered with HRTEM CHAIN-WIDTH DISORDER IN PYRIBOLES •.• Chain-width
disorder
194 197 197 202 204 204
207 208
in amphiboles
Amphibole asbestos Nephrite (actinolite jade) Acicular and massive amphiboles
ill
208 208 210 210
Page CHAIN-WIDTH
DISORDER
Chain-width Chain-width TERMINATION
IN PYRIBOLES,
disorder disorder
continued
in wide-chain in pyroxenes
pyriboles
211 213
DEFECTS •..
214
Chain terminations Zipper terminations Termination rules
214 217 220 220 222
Rule #1 (the "eubchai.n rule") Rule #2 (the "odd-even rule") POLYSOMATIC
REACTIONS
IN BIOPYRIBOLES
••
223
Mechanisms of polysomatic reactions Kinetics of polysomatic reactions Distinguishing primary growth microstructures microstructures CONCLUSION
AND SUGGESTIONS
ACKNOWLEDGMENTS. CHAPTER
. .
4 REFERENCES
INTRODUCTION
ASBESTOS MINERALOGY
• • . • • • • • •
Structural THE SURFACE
HABITS
OF AMPHIBOLE
defects
STRUCTURE
OF ASBESTOS
238 240 242 242 244 245
ASBESTOS
in amphibole
asbestos
OF FIBERS.
AND WHISKER
Tibor Zoltai
238
246 249 254
Fiber length and strength Fibers, crystals and fragments Polycrystalline wires and aggregates ORIGIN
233
237
The columnar growth habit The reticulated growth habit The radiated growth habit The massive-fibrous growth habit Isolated fiber growth habit Synthetic asbestos and whiskers STRUCTURE
231
235
AND ASBESTIFORM
THE UNIQUE
from reaction
234
CHAPTER 5. AMPHIBOLE
FIBROUS
FOR FUTURE WORK
223 228
FIBERS.
263 265 265 267
Whisker growth Origin of asbestos
267 269
CONCLUSIONS ••
271
CHAPTER
274
5 REFERENCES x
Page
CHAPTER 6. THE GEOLOGIC OCCURRENCES AND HEALTH HAZARDS OF AMPHIBOLE AND SERPENTINE ASBESTOS Malcolm Ross INTRODUCTION
279
The problem The dilemma THE ASBESTOS
279 280
MINERALS.
281
Amphibole asbestos Chrysotile asbestos ASBESTOS
281 283
IN THE WORLD ECONOMY.
284
Early beginnings The modern industry Modern asbestos uses MAJOR GEOLOGICAL Amosite
OCCURRENCES
and crocidolite
284 286 287 OF AMPHIBOLE
ASBESTOS
in ironstones
• • . •
of South Africa
Transvaal asbestos field Cape asbestos field Formation of banded ironstones
OCCURRENCES
OF AMPHIBOLE
Anthophyllite asbestos Tremolite asbestos Actinolite, amosite, and crocidolite MAJOR OCCURRENCES
OF CHRYSOTILE
Type I deposits Type II deposits
ASBESTOS
ASBESTOS
. . . . .
296
of southern Africa
OF ASBESTOS to asbestos
Production Geology Asbestos and health
296 299 299 300 300 301
exposure
Asbestos trades workers Asbestos miners and millers Mortality comparisons, trades vs mines Crocidolite exposure SUMMARY.
294
asbestos
Type III deposits
Diseases related Epidemiology
. . . . . • . . ..
291 292
294 295 296
South Africa and Swaziland Zimbabwe HEALTH HAZARDS
288
288 290 290
Crocidolite in ironstones of Western Australia Anthophyllite in Alpine-type ultramafic rocks of East Finland MINOR GEOLOGICAL
287
301 304 305 308 310 314 316 316 317 317
Page CHAPTER 6, continued ACKNOWLEDGMENTS ...
319
CHAPTER 6 REFERENCES
320
CHAPTER 7. SUBSOLIDUS REACTIONS AND MICROSTRUCTURES IN AMPHIBOLES Subrata Ghose INTRODUCTION
325
THERMODYNAMICS AND KINETICS OF THE Fe2+-Mg2+ ORDER-DISORDER REACTION IN FERROMAGNESIAN AMPHIBOLES .
325
Mg-Fe in cummingtonite and actinolite Mg-Fe in anthophyllite and the cooling rate of rocks Mg-Fe in sodic amphiboles PHASE TRANSITIONS IN FERROMAGNESIAN AMPHIBOLES. The P21/m ~ C2/m phase transition in magnesium-rich cummingtonite Nature of the structural changes Possible anti-phase domains in cummingtonite Anthophyllite-cummingtonite phase relations MISCIBILITY GAPS AND EXSOLUTION TEXTURES IN AMPHIBOLES Introduction Actinolite-hornblende Hornblende-anthophyllite Actinolite (tremolite)-anthophyllite Hornblende-cummingtonite (Tremolite) actinolite-cummingtonite Tremolite (actinolite)-riebeckite Actinolite-glaucophane Hornblende-glaucophane Glaucophane-riebeckite Richterite-magnesio-riebeckite Anthophyllite-gedrite Arfvedsonite-cummingtonite Tremolite-richterite Conclusions THE THERMAL DECOMPOSITION OF AMPHIBOLES INTO PYROXENES AND OTHER PHASES. Crocidolite and sodic amphiboles Tremolite Grunerite (and amosite) ACKNOWLEDGMENTS
325 332 337 338 338 338 339 340 341 341 344 345 346 346 350 352 352 353 353 354 357 360 362 363 364 364 365 366
_ _ _ _ _ _ _ _ _ _ _
CHAPTER 7 REFERENCES . . . . _ _ _ _ _ _ _ _ _
368 369
For contents of Volume 9B, "AlfPHIBOLES: Petrology and Experimental Phase Relations," see front cover. xii
in
REVIEWS
MINERALOGY
FOREWORD It was immediately of America
preceding
in 1965 that the first mineralogical
the American
Geological
Institute.
J.V. Smith of the University participated
that:
spersed.
They were duplicated The thirty I recall
David
Stewart once saying
The Mineralogical
Society
of America
revived
geologists.
Volume
the short course "movement"
in Miami.
This year
at Erlanger,
Kentucky,
one hundred
geologists,
many of them with excess baggage
No less than two (2) volumes by no less than seventeen
totalling
(17) authors.
It was attended
by
1 of "Short Course Notes,"
was 284 pages long and represented
course on amphiboles
copies
in small 3-ring
that that would be an appropriate
on sulfides
number
threaten
and assembled
int
But such is not to be, for mineralogical
It is in its third printing.
approximately
The notes for that
institutionalized.
and workshops
one hundred
Sulfide Mineralogy, authors.
literature.
have become
in 1974 with lectures approximately
geologists
with a few hand drawn figures
on Ditto machines
contributions
convened
by David Veblen,
but the published
charges
from six
(1981), participants
in the will
"notes" may
on their return flights.
750 pages were prepared
for this event
The first press run will total 2 x 4501
(up from 1 x 1500 copies in 1974), with the first 1450 copies of volume:
9A and 9B being Furthermore,
sent to all of M.S.A.'s
the ink is unfading
institutional
and library
subscribers.
and the covers are plastic-coated!
Paul H. Ribbe
Series Edi tor Blacksburg,
N.B. -
1:
by
to forty pages of notes have long since faded to unreada-
fate for all geological short courses
was convened
one hundred
and workshops.
outlines
Societ
"short course" was sponsored
approximately
discussions
skeletal
binders.
of the Geological
That course on feldspars
of Chicago;
in the lectures,
course were exactly
bility.
the annual meetings
Additional
Mineralogical available
copies of this and other volumes
Society
of America
at a moderate
under
the title "Reviews
cost (about 2¢ per page).
iii
now published
VA
by the
in Mineralogy"
See details
are
on page ii.
PREFACE
and
This volume of "Reviews with the Mineralogical
volumes,
in Mineralogy"
Society
Other Hydrous Pyriboles,
ACKNOWLEDGMENTS
of America
Fall, 1981.
was prepared
directory
(it is hoped, however,
in some respects
to the geological
sciences).
lection
appears
from a combination
amphiboles
themselves
complexity behavior
papers are relatively easily and quickly (and lengthy)
chemical
of phenomena.
amphibole
probably
researcher.
with justification,
that they would never have stopped writing
literature
that
others are exhaustive
that may not be digestible
even the most dedicated
of petrologic
while some of these
of the published
by students,
The
their structural
and diversity
In addition,
brief summaries
can be consumed
discourses
some geologists,
variability
brief description.
is more read-
The length of this col-
must accept most of the blame:
and resulting
preclude
to result
the Manhattan
that the content
able and relevant of papers
and
Had it not been split into two
9A and 9B, it would have resembled
telephone
in conjunction
Short Course on Amphiboles
in one sitting by
Finally,
it appears
love amphiboles
that
so much
had there been no publication
deadline. The extremely lication
short time between
of "Reviews
in Mineralogy"
of their fields ensure search results. tably results publication included
universe,
a collection
papers presented amphibole
into Volume
the sequence notions
of reviews
of presentation
of
of this sort cannot claim to give
of a topic, it is hoped that the areas of active
and Other Hydrous Pyriboles
9B, Amphiboles:
is encouraged
Petrology
to purchase
there is a hefty dose of petrology for example)
that are
the order in which papers were received.
9A, Amphiboles
Everyone
inevi-
of order in the amphibole
The papers have been split in a somewhat
and Volume
knowledge
however,
for any such errors
here do review most of the important
research.
Relations.
Thompson,
In addition,
to all aspects
Mineralogy,
because
of the "Reviews,"
apologize
not only the editors'
coverage
intimate
the very latest in re-
that might be caught in a more leisurely
the editors
but also somewhat
Although exhaustive
fashion
The rapid production
in this volume.
papers reflects
of papers and pub-
and the authors'
that the papers reflect
in a few errors
process;
the preparation
-
and Experimental
Phase
both volumes, however,
in 9A (witness the paper by
and not a little mineralogy
iv
arbitrary
in 9B.
Colleagues
too numerous
these volumes
of "Reviews
couragement.
Institutional
versity,
The Johns Hopkins
Institute readable
copy, especially
able assistance for producing reproduced. maintaining
invaluable
through
in the preparation
by Arizona
and Virginia
their papers by the first
Elliott
these volumes
of Blacksburg,
the final manuscripts. as local organizer
and most obviously
for proofreading
sense of humor throughout.
and Rachel
for typing
copy from which
I thank Sarah Veblen
a much-needed
assistance
for producing
Above all, I thank Paul Ribbe for being of invalu-
the camera-ready Finally,
State Uni-
Polytechnic
I thank the authors
those who submitted
of
their advice and en-
during all phases of this endeavor
Haycocks,
responsible
assisted
support was provided University,
and State University.
(of many) deadlines!
Ramonda
to mention
in Mineralogy"
Margie Virginia,
Strickler, were
John Grover provided
for the Short Course
itself. David Veblen Baltimore, MD September 1981
v
were and for
Chapter
CRYSTAL CHEMISTRY
1
of the AMPHIBOLES
Frank C. Hawthorne
INTRODUCTION
An appreciation damental processes.
This premise
amphiboles. geneses
of the crystal
to our perception
of a mineral
has particular
Few other mineral
validity
understanding
derive the formula essential
tures of tremolite of diopside
Warren
chemical
homology
homovalent
the chemistry,
and diffraction
(1930) and Kunitz
and heterovalent
patterns,
emphasizing
substitutions
Since 1965 there have been significant electron
spectroscopy.
proliferation
The resulting
data has led to a substantial A synthesis
increase
Warren
amphibole
that
properties
(1929) and
also extended
to
and solved the struc-
(Warren and Modell, and
the importance
to the chemistry technological
microprobe
advances
analysis
of structural
is presented
and chemical of the am-
here.
formula may be written
Na,K
C
Mg,Fe
B
Na,Li,Ca,Mn,Fe2+,Mg
T
Si,Al
2+
in the
and resonance
AND NOMENCLATURE
A
of both
of this group.
in our understanding
of this information
CLASSIFICATION A standard
physical
(1930) showed the structural
of the amphiboles,
is an
by analogy with the known structures
fields of x-ray diffraction,
phiboles.
that hydroxyl
and the amphiboles.
and anthophyllite
as
It had long been recognized
between
(Warren and Bragg, 1928) and enstatite
1930b).
quite as rapidly
(1930a) showed that this relationship
the unit cell dimensions
our
(1916) was first to
when he recognized
and paragenes·is of the pyroxenes and Modell
Schaller
of that mineral.
there was a strong relationship
Consequently,
has not progressed
minerals.
of tremolite
constituent
the
groups show such a wide range of para-
of the amphiboles silicate
group is fun-
in petrologic
when considering
and none show as wide a range in chemistry.
for the less complex
Warren
chemistry
of the role of such minerals
,Mn,Al,Fe
3+
. ,Tl
Table
1.
Prefixes
and
Adjectival
alumino-
see Tables
chlor-
when ci > 1.00
('\04% Cl)
chromium-
when Cr > 1.00
('\09% Cr 203)
ferri-
when
ferro-
see Tables
3
Fe
Hodifiers
r-..9%
).1.00
when F ~ 1.00 when OH>3.00
manganese-
when
z.!n).
magnesio-
see
Tables
oxy-
when
potassium-
when K ~ 0.50
Fe 0 ) 2 3
except
("~lOi; MnO)
2,
3 and
Table
is
except
also
!J"
see
zinc-
when Zn > 1. 00 ('\05% ZnO)
in
as
('\,10% Ti0 ) 2
'Iu b Le s
0.25-0.99
=
i te
ferroan
see
Figure
lithian
when Li ~O.25 ('1,,0.4% L1 0) except 2 is used for Li ?O.50 ('1,,0.8% Li 0). 2 and clinoholmquis ti t e
2 (only
magnesian
see
mang ano an
when
p lumb ian
when Pbo,.O.08
potassian
when K
silicic
see
Figure :c
=
Figure Table Table
in
2 (only
with
pargasite
with
0.25-0.99
hastingsite
0.25-0.49 2 and
('\01.3-2.7% Table
('\02.5-10% TiOi)
0.25-0.99
of the amphiboles
that is sufficiently
having
basis.
flexible
hornblende)
end-members
~n
containing
The need for a precise
to encompass
the group has long been apparent
report of the I.M.A. Subcommittee
chemistry,
in
has given rise to a proliferation
names that has no systematic
unit calculated
hastingsitic
lithian
K 0) 2
('\01.2-5% ZnO)
such a nomenclature.
hornblende)
3
=
within
amphiboles
('\01.1% PbD)
when Ti = 0.25-0.99
variations
pargasitic
and
when Zn
of mineral
in alkali
alkali amphiboles when Not used with holmquistite
("'-'2.5-10% MnO) except
titanian
nomenclature
except
and in
zincian
The complexity
kaersutite
('\02.3-9% Cr 0 ) 2 3 C"'6.8-n Fe203)
0.75-0.99
has tings
see
M:1
modifiers
and
see
containing
2 and
=
subsilicic
end-members
7.25
Subsilicic
5.75>
Calcic amphiboles: ferro-tschermakite
to
calcic
('\03.5%Na 0) 2
1. 50 ('\09.5% CaO) (Na+K) A.0. 50
S1 ) 5.50
and ferro-tschermakitic
prefixes
precede
fixes aluminoname; otherwise,
Alkali
amphiboles:
tschermakitic hornblende,
are used is not fixed.
the prefixes
Neither
as hastingsite
precede
the order in which
the prefixes
Optic orientation
implies high Fe3+.
7
the fundamental
the preamphibole
are used is not fixed.
may be indicated
the symbol G, C, 0 or R for the four possible
otherwise,
ferri- nor
As with the calcic amphiboles,
and ferri- immediately
amphiboles:
hornblende,
the word tschermakite;
should be used with hastingsite,
Sodic-calcic
amehiboles
With tschermakite,
and ferri- immediately
the order in which ferrian
te
te
ts chermaki
Al umino-magnes
alumino-
?
cs cher.naki
Ferri-
(OH) 2
orientations
by prefixing (Borg, 1967b).
s"
;:: o
o'" OJ .~
N N
o
co
....
"'v
00
"'
µ.
N
.....
N
.",..,
~ "
µ.
be
~,
"
'"'N z
Z
oj
"
7.
o u
"
....
"
u
...>
iii ...." ~, " u
-5 ..,
.....
"
...>
u
'" V
~ ~
Z
r-r
.0 8
;::"
,., V
0
"0
0
'" "' '6 V
~,
N
V
V
"
.....
e
jl
N
'" '" 0
0 N
N N
N
0
....
U>
U>
00
00
N
e,
....
N
r-r e
00 V
;?
;::
;::
;::
0
0
0
0
0
N N
.... 4, 4__i- .~ "'....",- ...."
."'..."
N
;::
N N
0
N 0
.....
- U> NM N V V
rr,
co
..... -c
-c
1f)C'111"\
U> 00 V
.~ .....
.0 0 .... µ.
Z
Z
U
U
co
M
Z
NMNMC'1 V
V
." ....:rc--r..;tN·
-cr
U> N
..;r
V
."
r; 0(;
Z
_" C'J (") V
Z
Z
u
V
µ.
rc
...:;:tC'J...:::tN 00 V
-::tN
V
MNOO V
u
u
U
Z
U Z
U Z
U
Z
MN
C")
V
c,
""
N
N
rl
.."
00
M
V
Z
Z
Z
Z
U
U
U
U
Z
Z
Z
Z
u v
"0 ~
V
v
.... 0
V
....!':
"
.c u
~
v
V .0
u
....
~ v
8 V
..; v
.....
.0
"
H
e
....
U
U
.....
",
U
0 0
...;
...
U H .~ c.....
"0 0
'"
-c
V
u
, u"O
...
0-
"
0
" 0 uw
.c
.c
u
..... "0
"0 0 U>
V
.....
.....
co
ev
N
0
,,, ....."' ... ... -c "' ,~ ..... ..... on ... '"~, v -c " >::"' ""... ... ... ~on "" ';d eo eo co ~ ro ~ " ~ >:: ... ... ~ ... >:: .... z z ~" ~" " " " " " " " " " " " "z z" u ~" u" ~ " u " " " " u ~ u-o ~ " " " " " " " " "
.c
.!l1:8
0
0
'"c-r
V
o.-~
;::
;::
0
0
c,
"
0
N N
00
0
....
;::
N
-, ;:: ;::'" ;:: 0 S 0 ~, e,e,
8 "0
0 W
u
...."
u
~
V
u
.c u
;;!
.C
u ....~
V
v
....u
.c
....
.c u
,
U
....0
0 .
I
...,
.... ~ ~ ... ..." " I 0
u
I
u
µ.
0
...." 8
"
.....
."
....0, I 0
....0
~ " ~ ~ "
..... I
0
µ.
....u V u
....
.c
U
, 0
....
v
....u ..'",
~ ~ " ... 0
V
,0 I 0
~ .... ~ ~ ~ " .....9 .... " ~ ~ ..... "~ ,,," " ..." 0
0
I 'd
V 'H I 0
v
.0 I 0
0
8
.."
I 0
..,
u
....'"
u .
....'"
~ "" ... ~ ~ 0
.0 I
.
...v
8
....'"
G
s: eo. u
3
-"
~ " .'"..." .o ".... ~ ~ ...v "~ ..." .... ...~ '"v " v >~ " I
I
I 0
I 0
be
v
0
0.-
0
µ,
~
0
.c
",
....
0
8
"
.....
" ." I 0
'"v
"eo
'""
u
....
v
u
0
0
........... U
.~
v
.... ..~, .c~ u
V
u
0
0
.c 0.0
u
"
-"I
....
0.0
u
"
-"I 0
.... ~ ~ 5 v 0
rl
I~
-0
'ij ~ " .... .... v ~ ~ 8 ...v "~ ru ~ " " .... .... '"v ....r: ~ 8 ~ ,.. "" ....." u I
V u
u
'd
B
I 0
u I
u I 0
0
be
V
."
la~
"
u I 0
....0
e .....
"
"
I 0
....sn v
0 be
"
:E
u v
'" V
.......v X
~
0.
I 0
....0
3
.....
.."
General
considerations
For amphiboles from optical to allocate
that are not precisely
properties a precise
without name.
chemical
characterized
analysis),
(e.g., identified
it is not possible
In this case, the assigned
amphibole
should be made into an adjective
followed by the word amphibole,
tremolitic
amphibole.
amphibole,
pargasitic
be used for calcic amphiboles erties and not confidently For the various involve
the precise
asbestos,
identifiable
asbestiform mineral
of the mineral
When the approximate composition,
purpose,
crocidolite
amphiboles,
amphibole
prop-
usage should
thus, anthophyllitethis volume).
Where
is known but not its precise
name should be made into an adjective asbestos.
is used to cover alkali amphibole
For this
asbestos
in general,
are to be followed when the precise
com-
is known.
A large number
of amphibole
names have been formally
1978) and should not be used; this included blende,
ferrohastingsite
ple considering
and carinthine.
the complexity
in rapid and unambiguous
The essential
naming
feature
of corner-linked
tetrahedra stoichiometry
merization
CRYSTAL
(T40
on such factors
chain.
structure
infinitely
is a double chain
in one direction
The direction
of infinite
and
poly-
the Z-axis of the amphibole
The actual value of the repeat distance
as the occupancy
of the unit cell and is dependent
of the tetrahedrally-coordinated
of the tetrahedra;
only minor perturbations
(Si4011)oo
)oo.
is the a-dimension
sites and the stereochemistry
is fairly sim-
group and should result
STRUCTURES
11 unit defines
cell in the normal orientation. in the Z-direction
(Leake,
horn-
of amphiboles.
that extends
of the double-chain
abandoned basaltic
This nomenclature
of the amphibole
has the general
barkevikite,
of the amphibole
THE AMPHIBOLE
produce
is to
alone may be appropriate.
thus, anthophyllitic
the above recommendations
position
mineralogical
(see chapter by Zoltai,
nature of the mineral
the assigned
hornblende
and/or optical
as near to an end member.
is not known, asbestos
by the word asbestos;
whereas
Similarly,
by physical
name followed by -asbestos;
actinolite-asbestos
the nature
followed
identified
name thus,
It is convenient
however,
from the ideal value of ~5.3 to recognize
9
cation
these factors
two different
A
for an
types of
1 ~~~~
1 Figure 5. The crystal structure of C2/m amphibole projected down [OOlJ. show the I-beam units of the structure. From Cameronand Papike (1978).
oxygen anions parallel
the oxygens
between
adjacent
All oxygens
tetrahedra
together)
oxygens.
while
Oxygens
cations are called bridging
and here are denoted
(link-
as O(br), while
cation are called non-
to one tetrahedrally-coordinated
and here are denoted
lie in two planes
lying in the plane containing
lying in the other plane are called apical
4 oxygens bonded
bridging
The oxygens
are called basal oxygens,
tetrahedra
to two tetrahedrally-coordinated
ing two T0
A)
element.
to the chain direction.
the linkages
bonded
in this double-chain
Shaded areas
as O(nbr).
The (T 0 )oo chains are linked by medium-sized (ionic radius 0.53-0.83 4 11 divalent and trivalent cations that bond to the O(nbr) anions of the
chains.
Two types of inter-chain
strip of divalent
and trivalent
linkage may be recognized. cations
layers of apical oxygens belonging orthogonally
to the plane of the basal oxygens.
are staggered
in the Z-direction
divalent
and trivalent
cations.
arrangement
The adjacent
the amphibole
formula.
together
In order to complete
of adjacent
the coordination
of
to add another anion in
double chains are tightly
unit, an I-beam, 10
double chains
this is the monovalent
Thus, these adjacent
and form a modular
two each other
around each of the linking
in the center of this strip, it is necessary
anion to the plane of the apical oxygens;
bonded
between
that adjoin
so that the apical oxygens
chains assume a pseudo-octahedral
the cations
are intercalated
to double chains
First, a
that plays an important
role in model amphibole 1970; see chapters
structures
by Thompson
(Thompson,
and Veblen, this volume).
The second type of inter-chain together valent
in a three-dimensional
cations
basal oxygens
cations,
together
of adjacent
the modular
The B cations
the B-type described whereas
define a strip of edge-
of as a strip of edge-sharing
thus far, the structure
adjacent
cations
The inter-chain
T-type
individual
linkage
cations all bond to non-bridging
cations bond with the non-bridging
to the central
cation.
back-to-back bridging
double
oxygens.
actual position figuration
Figures
cations
anions to which
requirements,
The A cations
double chains orthogonal structure
are situated within
assumed by the A-type
of the surrounding
of local stereochemical amphibole.
of which
requirements.
is a function
and the number
additional
schematic
and con-
linkage between
projections
the
are a function
and vary with the chemistry
thus provide
the
by 12
this cavity;
to the plane of the double chain.
is one of great elegance;
in a dis-
Between
it is bonded
anions.
are neces-
These anions are arranged
chains is a large cavity that is surrounded The A cations
linkage
and bridging
sarily bonded
the exact configuration
by
anions
by eight anions, not all of which
cation and local structural
I-
provided
are surrounded
torted square antiprism,
cations.
of the octahedral
The B cations
of the central
sand-
by the A and B
from the second type of inter-chain
The C-type
the B-type
of ~and
linkage both within
I-beams.
differs
above.
consists
at the margins
additional
Thus, an
octahedra
tetrahedra.
units is provided
are situated
they provide
beams and between
and trivalent
in the Z-direction.
infinitely
units
and trito the non-
These divalent
that extends
linkage between
cations.
I-beams.
two double chains of corner-sharing
As described
strips, where
The divalent
anions,
octahedra
Further
joins these modular
(Fig. 5).
with their coordinating
I-beam may also be thought wiched between
linkage
array
at the edges of an I-beam unit link laterally
bridging
sharing
1970; Papike and Ross,
of the adjacent
The complete are shown in
5 and 7.
Choice of axes The original
crystal
(1929) was referred phological
convention
structure
determination
to an I-centered of defining
for tremolite
cell and conformed
to the early mor-
B as the acute angle between
11
by Warren
the X and
• ~~~
'1 a
= ~.~
bl
=
be
c1
=
ee
e
-------"112)
----,
"............ --0 1
II
1
sin
Be
=:
Some confusion and Zussman,
subsequently
1961).
symbols
notation.
orientation. crystal
for the monoclinic
cell with
1955; Heritsch
S
obtuse;
+
between the I- and CModified from Whittaker
this point
work was done before
Current
the intro-
axes.
into the
parameters
were
crystallographic
B
system defines
the X and Z crystallographic
and Reichert,
r.:'l
but the unit-cell
convention
(Zussman,
2aIcl cos 51
cos Be
and the space group was reported
still given in the I-centered
Heritsch
+
This was translated
form C2/m by later workers,
angle between
+
arose concerning
Warren's
of the Hermann-Mauguin
as 2Ci-3 using the Wyckoff
....
lJ1
Figure 6. The geometrical relationships centered cells of the clinoamphiboles. and Zussman (1961).
standard
2acec
e21
I
~Ol~
duction
+
I
------
(Whittaker
e~
Ic
...... '.....
the Z axes.
+
as the obtuse
Several
later studies
et aZ., 1960; Heritsch and Kahler, 1960;
1960) report atomic coordinates
in these studies,
in an I-centered
the signs of the z coordinates
should be reversed. Here, all crystallographic C-centered lographic
cell with axes with
tween the I- and C-centered Principal
structure
The extensive
to a
cells.
morphological
studies
group symmetries
has been standardized
types
shown that amphiboles and Warren's
information
S obtuse. Maintaining a right-handed set of crystalS obtuse, Figure 6 summarizes the relationships be-
investigations
occur in both monoclinic
and orthorhombi.c varieties,
showed that these were related
C2/m and Pnma, respectively.
the past 20 years has unearthed ferent space groups.
of the 19th century had
structures
More detailed work during
three more structural
Gibbs et aZ. (1960) reported 12
with space
variants
with dif-
the synthesis
of
Table
6.
Site-Nomenclature
C2/m
~/m
T(l) T(2)
T(lA) T(2A)
-te trahedrally coord ina ted
sites
Scheme
T(lB) T(2B)
ill M2 M3
ill M2 H3
M(4)B
M4
M4
cubic an tiprismatic e t tes
M(4)
M(4)
M(4)A
A
A(2)
non-bridging anion sites
O(lB) 0(2B) D(3B) 0(4B)
bridging anion sites
0(5) 0(6) 0(7)
0(5A) O(6A) 0(7A)
0(5B) 0(6B) 0(7B)
o
protoamphibole, Pnmn; Gibbs
TlA TZA
M(3)
O(lA) 0(2A) O(3A) 0(4A)
a new orthorhombic
O(l)A O(Z)A
Deer et aZ. (1963) postulated
TlB T2B
A O(l)B O(2)B
0(3) O(!')A
O(4)B
0(5)A O(6)A
0(5)B 0(6)B 0(7)
Tl T2
A
OIA 02A 03A 04A
OIB OZB 03B 04B
05A 06A 07A
0SB 06B 07B
01
02 03 04
os 06 07
to describe the positional disis described in the section on
amphibole
(1964, 1969) subsequently
Pnrnn
M(l)B M(2)B
M(l)A M(2)A
A
Pnma
T(l)B T(Z)B
M(l) M(2) M(3)
0(1) (Z) 0(3) 0(4)
Types
T(l)A T(2)A
M(l) M(Z) M(3)
cavity*
Structure
PZ/a
*the more complex nomenclature used order of cations occupying this site the A-site.
ture.
Amphibole
octahedrally coordinated si tes
[12J
Fe-Mg-Mn
for
with space group symmetry
refined
the protoamphibole
the existence
struc-
of a magnesium-rich
amphibole
with P21/m symmetry. Bown (1966) subsequently reported such an amphibole, and the structure of a tirodite P2 /m was 1 refined by Pap ike et aZ. (1969). Moore (1968a,b) reported the existence of a peculiar dimensions structure
and space group
fide
analysis
of the structure amphibole
Site nomenclature
congruence general possible schemes
between
between analogous
site-nomenclature structures
of this mineral
The unit-cell
with an amphibole-type
Subsequent
solution
(joesmithite)
and
showed it to be
double chain (Moore, 1969).
inter-structure
comparison
it is desirable
to have a site-nomenclature
structure
sites in different
would have
structures.
some sort of A completely
these restrictions
the same type of basis for the pyroxenes
(Megaw, 1956).
of structural
types but maintains
that would satisfy
that have been derived
and the feldspars
was not.
Sweden.
in amphiboles
in the amphiboles,
that differentiates
from Lgngban,
with a beryllo-silicate
In order to facilitate features
mineral
(P2/a) were compatible
but the chemical
refinement a bona
amphibole-like
for all
as the nomenclature
(Burnham et aZ., 1967)
Such a scheme would also be extremely 13
cumbersome
and is not really necessary
tural varieties systematic
are discovered.
(Table 6).
structure
type.
(1973a,b)
the monoclinic
the presence consistent
and orthorhombic
1970; Papike
and Ross, 1970) which
the parentheses
et al. (1973) and
by changes
amphiboles
vari-
that correspond
involved.
may be indicated
is thus adopted
by
This is
of the Pnma amphiboles
of the Pnmn structure
to
The difference
in the site symbols.
the current nomenclature
The site-nomenclature
here is not as
for the other structural
of the structures
or absence of parentheses
with
struc-
but is convenient
used by Robinson
from this nomenclature
the space group differences
additional
is adopted here for the C2/m amphibole
The site-nomenclatures
ants can be derived
developed
and feldspars,
The site-nomenclature and Grundy
between
The scheme
as those for pyroxenes
Hawthorne
unless numerous
(Finger,
in the current
scheme.
(Gibbs, 1969) is changed;
are not used and the Si(l) and Si(2) sites become
the Tl
and T2 sites.
For the P2l/m structure type, parentheses were added to the nomenclature scheme of Papike et al. (1969, Fig. 2). The site-
nomenclature
scheme
for the P2/a structure
ble that of the other amphiboles numbering
was adjusted
bole structures.
to correspond
structure
those with
the suffix B.
type is monoclinic;
this structure parentheses
with
the numbers
sites of all the various The C2/m amphibole
in the other amphipairs of atoms,
were labelled
by addi-
are used because
this
in order to distinguish
structure
types are summarized
sites in
in Table 6.
structure
ing that this must be the most flexible, structures.
The site
sites in the P21/m structure type, the only in the P2/a structure type. The
This is the most common of the amphibole
these
revised.
the larger value of the y-coordinate
Parentheses
however,
type from similar
enclose
equivalent"
value of the y-coordinate
tion of a suffix A while were labelled
with numbering
For the "pseudo-mirror
those with the smaller
(Moore, 1969) does not resem-
and was completely
A schematic
ture type is shown in Figure
7.
structure
or chemically
polyhedral
types, suggestcompliant,
representation
There are three non-bridging
atoms:
0(1), 0(2) and 0(4); of these, 0(1) and 0(2) are apical oxygens is a basal oxygen.
There are three bridging
all of these are basal
oxygens,
anions:
and 0(4)
0(5), 0(6) and 0(7);
and 0(5) and 0(6) bridge
14
of
of this struc-
along the length
J
1 b---------oot
Figure 7. The C2/m amphibole structure projected elements are shown. From Hawthorn.e (1982).
onto (100);
the space group symmetry
r 1 b
Figure 8. The P2l/m amphibole structure projected metry elements are shown. From Hawthorne (1982).
15
onto (100); the space group sym-
of the (T 0 )oo double chain while 0(7) is the anion that links the two 4 11 pyroxene-like components of the double chains together. In addition, there is the 0(3) anion that is bonded
to three octahedrally-coordinated
cations;
wholly
02-.
the 0(3) site may be occupied
The anions are arranged
These layers are not close-packed cubic and hexagonal
or in part by OH, F, Cl or
in layers parallel
to the (100) plane.
but bear a simple relationship
close-packed
There are two unique cation
sites with pseudo-tetrahedral
coordina-
tion, the T(l) and T(2) sites, both of which have point symmetry T(l) site is coordinated whereas
by three bridging
the T(2) site is coordinated
anions.
T(l) and T(2) tetrahedra
linkages
II Z
as required
chains in this structure
and one non-bridging
by two bridging
alternate
are of the type T(1)-T(2).
type T(l)-T(l),
Ily
Cross-linkages
by the symmetry
of the chain.
are of the All tetrahedral
type are identical.
sites is 2 and the point symmetry and M(3) sites are coordinated
coordination,
of the M(l) and M(2)
of the M(3) site is 21m.
by four oxygens
Both the M(l)
and two 0(3) anions;
around the M(l) site, the 0(3) anions are in a cis arrangement around the M(3) site they are in a trans arrangement. by six oxygens
strip.
neighbor
These
tial ordering
and is situated
of C-type
in this structure
There is one unique cation site surrounded site with point symmetry antiprism, pancy.
but the actual
cation coordination
the back-to-back center of which
is postionally
of the octahedral
of the standard
chains is a large cavity surrounded
depending
on the chemical
formula.
composition
off the center of symmetry.
16
square
strip
Between
by 12 anions,
21m.
at the
This site mayor of the amphi-
studies have shown that the cation occupying disordered
the M(4)
in a distorted
may vary with cation occu-
is the A-site with point symmetry
may not be occupied Detailed
by eight anions,
at the periphery
by the B-type cations
for differen-
type.
The anions are arranged
The M(4) site is situated
and is occupied
bole.
2.
of the octa-
in next-nearest-
and thus afford great opportunity cations
whereas
The M(2) site is
at the margins
three sites differ significantly
configuration,
The
and two non-bridging
There are three unique sites with pseudo-octahedral
hedral
1.
anions,
along the chain; thus, all
the M(l), M(2) and M(3) sites; the point symmetry
coordinated
bo both
arrangements.
this cavity
The P21/m amphibole A schematic shown in Figure 0(4A), O(lB),
polyhedral 8.
representation
type is
O(lA), 0(2A),
are apical oxygens.
There are six bridging
anions:
the double chains and the re-
along the length of the (T40 )oo double chains. In 11 there are two anion positions, 0(3A) and 0(3B) that are coor-
to three octahedrally-coordinated
generally
occupied
cations;
by OH in this structure
these positions
coordi-
the T(lA) , T(2A), T(lB) and T(2B) sites, all of which have point
symmetry
The topological
1.
the coordination
labelled
non-equivalent,
shows a much greater
than does the A-chain,
that found in structures
in regard to the labelling
deviation
the A- and B-chains.
from an extended chain kinking
composition
M(l), M(2) and M(3) sites; the point symmetry is I and the point symmetry
sponding
strip are A-type
of the octahedral of tetrahedral
antiprism.
the
of the M(l) and M(2) sites The relative
configura-
to the corre-
note that the anions on one side of the anions on the other side Whereas
double chain in this structure
At the margins symmetry
coordination,
anions is similar
anions while
strip are B-type anions.
type of octahedral
to
with C2/m symmetry.
of the M(3) site is m.
sites in the C2/m structure;
the octahedral
The
chain configuration
being similar
There are three unique sites with pseudo-octahedral
tion of these sites and their coordinating
of the
double chains are crystal-
and are designated
of similar
The double chains
and retain the same linkage
the back-to-back
with the average
to
type,
A always bond to anions
cations.
symmetry
as the C2/m structure However,
are similar
sites in the C2/m structure
for the B-labelled
still have mirror
atoms of the chains. lographically
of their coordination
that cation sites labelled
A, and likewise
in this structure configurations
details
of the corresponding
with the restriction
B-chain
are
type.
There are four unique cation sites with pseudo-tetrahedral nation,
oxy-
bridging
addition, dinated
anions:
0(7A), 0(5B), 0(6B) and 0(7B); all of these are basal
gens, with 0(7A) and 0(7B) cross-linking mainder
of this structure
There are six non-bridging
0(2B) and 0(4B); of these, 0(4A) and 0(4B) are basal oxygens
and the remainder 0(5A), 0(6A),
structure
there are two types
type, there is only one
strip. of the octahedral
1, surrounded The cations
strip is the M(4) site, with point
by eight anions arranged occupying
in a very distorted
square
the M(4) site may not bond to all of the 17
surrounding
anions;
indeed,
to hinge on the bonding back-to-back
A-and B-chains
degrees of positional other structure examined
the existence
requirements
of this structure
type seems
of the M(4) cation(s).
Between
is the A-site, with point symmetry
freedom.
This site is identified
types, as it is unoccupied
the
m and two
by analogy with
in all P21/m structures
thus far.
The P2/a amphibole
structure
Only one representative covered.
Joesmithite
of this structure
is a beryllo-silicate
ture can be directly
related
schematic
representation
polyhedral
There are six non-bridging
amphibole
to its unusual
Note that the site nomenclature
type has so far been dis-
chemical
of joesmithite
is different
anions:
unusual
strucA
is shown in Figure 9.
from that used by Moore
(1969).
O(I)A, 0(2)A, 0(4)A, O(l)B, 0(2)B and
0(4)B; of these, 0(4)A and 0(4)B are basal oxygens apical oxygens.
whose
composition.
There are five bridging
anions:
and the remainder
are
0(5)A, 0(6)A, 0(5)B,
0(6)B and 0(7); all of these are basal oxygens, with 0(7) cross-linking the double chain and the rest bridging chain.
In addition,
along the length of the double
there is the 0(3) anion position
to three octahedrally-coordinated
that is coordinated
cations and is occupied
by OR.
There are four unique cation sites with pseudo-tetrahedral tion, the T(I)A, T(2)A, symmetry
1.
T(l)B and T(2)B sites, all of which have point
The topological
the coordination
coordina-
details
of their coordination
is similar
to
sites in the P21/m structure type. Whereas in the P21/m and Pnma structures the four unique tetrahedrallycoordinated sites occur in two distinct tetrahedral double chains, in the P2/a structure
of the corresponding
the four unique tetrahedra
chain, and all double
are all found in just one double
chains in this structure
type are identical.
There are five unique sites with pseudo-octahedral M(l)A, M(2)A, M(l)B, metry 2.
configurations
of these sites and their coordina-
to the analogous sites in the C2/m structure.
denoted by A and B bond to A- and B-type anions,
There is only one type of octahedral hedral
strip are the M(4)A and M(4)B
symmetry
2.
the
M(2)B and M(3) sites, all of which have point sym-
The relative
ting anions are similar Cations
coordination,
The anions
surrounding
strip.
respectively.
At the margins
sites, both of which have point each site are arranged
18
of the octa-
in a distorted
-----.1/4
I 1 c
10--------
b --------j
Figure 9. The P2/a amphibole structure projected elements are shown. From Hawthorne (1982).
onto (100);
the space group symmetry
I c
1 ~-----------b------------~ Figure 10. The Pnmaamphibole structure projected metry e Letaent.s are shown. From Hawthorne (1982).
19
onto (100);
the space group sym-
square antiprism, joesmithite
with all the anions bonded
itself.
is the A-site
Sandwiched
cavity,
surrounded
cavity is fully occupied center position, axis towards
between
by 12 anions.
by divalent
the A(2) site.
structure
this
that assume an ordered
off-
is along the two-fold
Be.
structure
This is the only structure orthorhombic
cations
cation in
double chains
In joesmithite,
This displacement
the T(l)B site that contains
The Pnma amphibole
to the central
the back-to-back
amphiboles.
type found thus far for naturally-occurring
A schematic
type is shown in Figure
10.
polyhedral
representation
of this
There are six non-bridging
anions:
OlA, 02A, 04A, OlB, 02B and 04B; of these, 04A and 04B are basal oxygens and the rest are apical oxygens.
There are six bridging
07A, 05B, 06B and 07B; all of these are basal oxygens, bridging
across the chains and the rest bridging
chains.
In addition,
which
to three octahedrally-coordinated 2by OR, F, Cl or 0 .
05A, 06A,
along the length of the
there are the 03A and 03B anion positions,
are coordinated
occupied
anions:
with 07A and 07B
cations
There are four unique cation sites with pseudo-tetrahedral
both of and are
coordina-
tion, the TIA, T2A, TIB and T2B sites, all of which have point symmetry The TIA and TIB sites are coordinated bridging
respectively
ically distinct
mirror
anions.
double
chains,
the A-chain
symmetry
and all of the intra-chain
in the C2/m structure
type.
A and B are coordinated
and the B-chain,
are analogous
a significant
have
to those
decrease
in
of each chain, the B-chain being more
than the A-chain.
There are three unique sites with pseudo-octahedral the Ml, M2 and M3 sites, with point symmetries Apart
that are con-
Both A- and B-chains
linkages
There is generally
rotation
by two bridging
There are two crystallograph-
from A- and B-type atoms, respectively.
the degree of ditrigonal kinked
Sites designated
to A- and B-type anions only.
1.
and one non-
anions and the T2A and T2B sites are coordinated
and two non-bridging
stituted
by three bridging
from the differences
sites is similar
in point symmetry,
to the corresponding
anions on one side of the octahedral other side are B-type anions. in this structure
coordination,
1, 1 and m, respectively. the coordination
of these
sites in the C2/m structure. strip are A-type
anions and on the
There is only one type of octahedral
type. 20
The
strip
At the edges of the octahedral metry 1, surrounded certainly
strip is the M4 site, with point sym-
by eight anions.
varies with
The actual coordination
cation occupancy
of this site and is possibly
of the more important
factors
The cations
this site may bond to bridging
occupying
A and B tetrahedral
have great flexibility they assume.
Between
point symmetry mayor
with regard to the possible the back-to-back
may not be occupied Unlike
significant
positional
depending
disorder
is shown in Figure
composition
11.
with this structure
and the only representative
polyhedral
representation
There are three non-bridging
anions:
type
01, 02 and
OS, 06 and 07; all of these are basal
In addition,
cations
which
and is occupied
There are two unique cation sites with pseudo-
coordination,
Tl site is coordinated
along the tetra-
there is the 03 anion position
to three octahedrally-coordinated
by F in protoamphibole.
the Tl and T2 sites with point symmetry
by three bridging
the T2 site is coordinated
and one non-bridging
by two bridging
There is only one symmetrically
distinct
and two non-bridging tetrahedral
1.
The
anions and anions.
double chain in this
type.
There are three unique
sites with pseudo-octahedral
Ml, M2 and M3 sites, with point symmetry coordination
hedral
amphibole
is a basal oxygen and the other two are apical oxygens.
double chain.
amphibole
type have yet
of this structure
across and 05 and 06 bridging
structure
in
of this structure
anions:
tetrahedral
this position
type.
oxygens with 07 bridging
is coordinated
of the
there seems to be no
There are three bridging
hedral
This site
(Gibbs et al., 1960) is a synthetic
symmetry
A schematic
04; the latter
chains is the A-site, anions.
on the chemical
amphiboles
Protoamphibole
type known.
geometry
structure
No naturally-occurring been found.
one
type.
this site
coordination
of the cations occupying
of the Pnma structure
with orthorhombic
occupying
A and B double
structure,
almost
anions of both the
by six bridging
the C2/m amphibole
The Pnmn amphibole
of this structure
Thus, the cations
m, that is coordinated
amphibole.
amphiboles
in the occurrence
double chains.
number
of these sites is similar
structure,
strip.
coordination,
2, 2 and 2/m, respectively.
to the analogous
and there is only one symmetrically
At the edge of the octahedral
the The
sites in the C2/m distinct
octa-
strip is the M4 site, with
11/4
1'/4
r~
11/4
~ -.-._.-
~ _._._-_ ----+
I
c
1"iI...
1
1.-
"
11\
.......
u
Yl
"--'
".
I
--
"""-'\:_'
•
10__------
r-f"""
..
2, surrounded
to the central M4 cation. M4 site still differs
..
"
"....
completely position
Although
only coordinated
significantly
by Li; however,
that it is positionally
Amphiboles
may be considered
layers of octahedra
cause the apical oxygens coordination 0/3 between
structure rhombic
Gibbs
coordi-
strip in that its
and bridging
of protoamphibole,
the
anions.
Between
by 12 anions,
2/m.
According
this site should be almost (1969) could not locate the in the structure
disordered
within
refinement
this cavity.
as layer structures
of alternate
±
are bonded
from the pseudo-octahedrally
of Li (a very weak x-ray scatterer)
Amphiboles
----+
..
by six anions,
is the A-site with point symmetry
analysis
occupied
and suggested
,
double chains is a large cavity surrounded
in the center of which to the chemical
..•••
by eight anions only six of which
cation bonds both to non-bridging
the back-to-back
I
----+
onto (100); the space group s~
nated Ml, M2 and M3 cation sites of the octahedral central
II
\MI
b -------04
Figure 11. The Pnmn amphibole structure projected metry elements are shown. From Hawthorne (1982).
point symmetry
1 \MI /I
0
.JP.:',.._o7~ii6
of the tetrahedral
of the octahedral adjacent
layers,
tetrahedral
types, this stagger
amphiboles
as ordered
require
stacking
and tetrahedra
sequences
along X
(Figs. 5 and 12).
layers provide
there is a stagger
Be-
the octahedral of approximately
layers.
is always
a regular
For the C2/m, P2 /m and P2/a 1 in the same direction. The ortho-
reversal
22
of this stagger
in order
IE--- C --+I
Figure 12. the direction
The Pnma amphibole structure of stagger of the octahedral
Table
calcic alkali
7.
Observed Represen
amphiboles, amphiboles,
magnes ia-cummingtoni
projected layers.
Amphibole Space ta ti ve Structures
sodie-calcic monoclinic
onto (010) j the at-roes indicate From Papike and Ross (1970).
Groups
and
amphiboles Fe-Mg-Mn amphiboles
te
j oesmi chi te
Pnma
orthorhombic
Fe-Mg-Mn
amphiboles,
holcquistite Pnmn
protoamphibole
lCinzburg (1965) however, Litvin clinoholmquisti!:e
2Woensdregt symmetry,
reports clinoholmquistite with P2/m s ymme t r-y e t eL. (1975a) have refined the structure of in the space group C2/m.
and Hartman
(1969) report
23
a ho r nb Lende with
P2 /m 1
;
z_} ~ ~
-, "'d."
__;;.
~ ""'0/
~ C2/m
Pnma
Pnmn
Figu~e 13. Schematic representation of the layer stacking sequences projected down Y for the various amphibole structure types. Modified from Gibbs (1966). The P21/m and P2/a sequences are the same as for the C2/m structure type, and are not depicted here.
that the resulting symmetry. tetrahedral
s
layers
(or simply ++-~),
sequence
is +c/3, -c/3,
stagger
for the
+c/3,
in Figure 13.
five known structural
are given above.
structure
variants
The amphiboles
types are listed in Table 7.
of other possible
adjacent while
in amphiboles
There are at present of which
of orthorhombic
type, the stagger between
This is summarized
Space group variations
these structure
to the requirements
is +c3,+c/3,-c/3,-c/3
type, the stacking
(or +-+-).
details
conform
For the Pnma structure
Pnmn structure
-el
structures
of amphiboles,
known to occur with
In regard to the existence
types, it is instructive
to consider
the
P2/a and P21/m structures. The P2/a structure has the same topological arrangement as the C2/m structure, but a different topochemical arrangement.
in cation ordering
that leads to the dif-
ferent space group; note that there is no major
It is the difference
change in the shape or
size of the unit cell and that the space group P2/a is a subgroup
of the
space group C2/m.
The P21/m structure has the same topochemical arrangement as the C2/m structure. Whether or not the topological arrangement is the same is a moot point.
However,
in symmetry
between
constraints
to allow local relaxation
topological
change in the structure
sequence. C2/m.
we can understand
these two structure
the difference
types as a relaxation
in the structure;
of symmetry
there is no major
type, such as a change in stacking
Again,
the space group P21/m is a subgroup of the space group Thus, we can identify the C2/m, Pnma and Pnmn structures as 24
principal
structure
considered
types in the amphiboles,
as simple
space groups
for amphibole
Pnmn structures subgroups
subgroup
without
derivatives
structures
derivative
All possible
from the C2/m, Pnma and
a change in shape or size of the unit cell are
of these space groups.
space groups
as none of these can be
of the other(s).
are not consistent
The possible
supergroups
with the amphibole
of these three
structure
without
change in shape and size of the unit cell, and thus all possible groups may be derived an introduction
to group theory and symmetry, as G
group and Q is the factor group
lattice
space groups
that are subgroups
direct product
derived
element
The two
structurally
distinct
in C2/m.
of symmetry
of Q.
1945).
Thus, all
For each of the space groups
H.F
pi
of Q are binary
with rank 2 are (I·e) where e is a non-
F, of Q with rank 4 may then be
All subgroups,
= Q. in this manner
space groups listed as subgroups
are listed
of C2/m are
as there are two symmetrically' distinct
This situation
are elements
types in addition involve
(Zachariasen,
of C2/m, Pnma and Pnmn derived
in Table 8.
symmetry
1968).
In each case, all elements
Q
H, of
of Q.
from the relation
Subgroups
see Yale,
p.Q, where P is the primitive
the rank of Q is 8; thus, the ranks of all relevant
of Q are 4, 2 and 1.
and thus all subgroups, identity
=
(for
of G may be formed by taking the semi-
of P and all subgroups
under consideration, subgroups
space
from C2/m, Pnma and Pnmn by group reduction
A space group G may be written
a
does not arise for
of this space group.
to the ones examined
cI
Other amphibole
here are possible.
centers of
as both centers structure
However,
they
a change in the shape and size of the unit cell or a change in the
stacking
sequence
along the X axis.
THE TETRAHEDRAL DOUBLE CHAIN There are at least two unique sites with pseudo-tetrahedral nation
in each of the amphibole
in local environment stereochemical moted studies addition
substitutions
from structure
differences
of intrinsic
in regard
types.
to structure
among the tetrahedra.
of these variations
to being
implication
structure
in relation
interest,
to cation ordering
in amphiboles.
25
Considerable
coordivariation
causes significant This in turn has pro-
to bonding
models.
In
such studies have considerable and constraints
on chemical
Table
8.
Subgroups
of C2/m, Pnma
*C2/m
and Pnmn
*Pnma
Monoclinic
(y)
*Pnmn
Orthorhombic
P2/a *P2l/m *P2/ a P2/m Cm
Pn2n
Pnm2l P2 ma l P2l2l2l
Pnm2l P2 mn 1
P2l2121
(x )
Monoclinic
P21
(x)
P2 /n l P2 l Pn
P2/n P21
P2
ic
Pn2la
Monoclinic
C2
Orthorhomb
Pn
Pa Monoclinic
Ptn
Triclinic
HonocLt m c (y)
(y)
P2/m
P2/m
P2
P2
l Pm
ci Cl
P:n
Monoclinic
(z)
Monoclinic
pI pI
P2/a
P2/n
P2
P2
Pl
Pa
l
l Pn
Triclinic
* reported
as
Triclinic
pI
pI
PI
Pl
amphibole
(z)
space
groups
The C2/m amphiboles Individual
Si-O bond lengths
have been several particular
bonding
attempts
range from 1.572 to 1.704
to rationalize
models.
Two models
these variations
A
and there
in terms of
for the Si-O bond have been con-
sidered.
covalent: bonding model. of a double bond involving orbitals)
for silicon
was extended
tetrahedrally
by Cruickshank
tals on silicon
extended
combining
tetrahedra
to tetrahedra
predictions
can be made
tetrahedra
(Cruickshank,
(1939) suggested (in addition
coordinated
with
showing
(by the e
the 2prr and 2prr' orbitals Assuming
some deviation
concerning
g on oxygen)
these arguments
from Td symmetry,
the stereochemistry
1961; Brown et aZ., 1969): 26
This idea
group theory arguments
d-p-rr bonds will be formed
of Td symmetry.
the formation to the 3s and 3p
by oxygen.
(1961) who used simple
to show that only two strong
polymerized
Pauling
the 3d orbitals
orbiin
can be several
of polymerized
(i)
Si-O(nbr)
bonds
providing
the Si-O(br)-Si
are usually
electronegativity (ii)
the shorter wider
(iii)
bonds
are usually
angles usually
chains of four C2/m amphiboles
decrease
In addition,
equations
was developed
relating
and showed
they correlated
bond lengths
to the
Si-O bond cations).
et aZ. (1971) who presented
to
and X:
+ 0.051 XO(l)
T(2)-0(2)
1.211
+
0.0029
+ 0.007 XO(2)
T(2)-0(4)
1.213
+
0.0026
+ 0.009 XO(4)
relating
bond length
=
to Si-O, P-O and S-O bonds by Gillespie
As the second
constant
tetrahedra
that are characterized
individual
Si-O bond
by Robinand Robin-
of this curve is
in a polyhedron
must be accom-
in the remaining
at ~l.S.
bonds
Consequently,
a larger
if the
irregular
between
their
bond length
than
(Fig. 14).
amount
of work has been done on Extended
(EHMO) calculations 1972a,b,c),
come to light as a result Si-O(br)
,
by large differences
lengths will have
tetrahedra
and Gibbs,
derivative
in some bond lengths of lesser magnitude
mean bond order is to remain
A considerable
+ 0.6[(2-n)/(n-l)
1.83 - 0.32/(1
an increase
verse
to bond order was deduced
For Si-O bonds:
panied by a decrease
(i)
that they conform individual
0.0029
n is the bond order.
ular Orbital
in the
+
Si-O
nathan
details
1.137
son (1963) and applied
more regular
the
in the order O(nbr)-Si-
of the non-tetrahedral
further by Mitchell
the T-O(nbr)
son (1963, 1964).
positive,
with
T(l)-O(l)
An equation
where
is not large;
associated
the steric
lengths with X (the mean electronegativity This approach
cations)
> O(br)-Si-O(br).
(1969, 1970) examined
above predictions.
bonds,
angles;
> O(nbr)-Si-O(br)
Brown and Gibbs double
Si-O(br)
tetrahedral
than Si-O(br)
of the non-tetrahedral
Si-O(br)-Si
O(nbr)
shorter
angle is not wide and X (the mean
stereochemical
relationships
of these studies:
is not a linear function
(Gibbs et aZ., 1972; Louis-
in silicates
and further
Buckel Molec-
function
of Si-O(br)-Si
of cos(Si-O(br)-Si);
27
but an in-
have
Figure 14 (to the right). Variation in mean bond length as a function of polyhedral distortion parameter 11 for C2/m amphiboles with little or no tetrahedrally coordinated Al.
I .~ o -b
Figure 15 (below, center). Variation in grand
o
•
.0
01.63 I
V
0.4
t:._
+ +
1.30 -I/eos
t
+
163
1.35
136
l(T-O(brJ-T)l---
138 140 142 (T-O(brl-T) (oJ __
left, below). Variation in individual 81-0 bond lengths as a function three O-Si-O angles involved in that bond for the C2/m amphiboles with coordinated AI.
of the little
1.65 1.65
.., o I
on
+
.4: (5 1
1.60
++
iii
t
1.60
106
108
110
non-bridging bri dQing bond
bond
++
0.46 0.4B 0.50 0.52 BOND OVERLAP POPULATION n (5;-01---
.I·IFigure 17 (to the right, above). fluor-tremo1ite (36) as a function molecular orbital theory.
• o
Variation in observed 81-0 bond lengths for of bond overlap population calculated using
28
tremo1ite extended
(30) and Hiicke.L
(ii)
Si-O bond lengths which
are a function
of the O-Si-O angles in
they are involved.
These predictions 15 and 16, where
are examined
for the C2/m amphiboles
it can be seen that the results
support
in Figures
the above con-
tentions. Cameron
and Gibbs
(1973) performed
(30)* and fluor-tremolite(36), are inversely Although
correlated
a valence
and Si-O(nbr) 1972).
with the Si-O bond overlap
changes
and Gibbs
correlated
bond directions
Thus,
is not inconsistent
for idealized
orbital
hybridization
standing 1968).
modeZ.
the chemical Bragg
inally developed
by Barlow Pauling
duced a set of empirical organic
crystals
and synthetic ful.
in silicates
inorganic
(Bent,
the hard sphere model of atoms orig-
rules to predict
the idea of ionic radius previous
stable configurations
observed
distortions
(Bragg
work and proin in-
in terms of ionin minerals
oxides and have been found to be quite success-
interest
the valence
cations,"
can
of the ionic model in under-
and developed
is Pauling's
where
second rule:
"In a stable
of each anion, with the sign changed,
equal to the sum of the strengths the adjacent
in Figure 17
model.
These rules have been tested extensively
Of particular
ionic structure,
observed
(1929, 1960) extended
and to rationalize
ion interactions.
of the cen-
bond in solids has long been recognized
and West, 1927).
along
in terms of
characteristics
bonding
The utility
(1924, 1926) extended
This
of Gibbs et aZ. (1972) that at
with the conclusion
in terms of a covalent
Bond-valence
environments
of two ordered populations
least part of the Si-O bond length variations be rationalized
acid molepopulation
in the bond.
and can be rationalized
the presence
the Si-O(br)
orthosilicic
angles involved
molecular
(Fig. 17).
(cf. Gibbs et aZ. ,
populations
with O-Si-O
in the non-equivalent
tral Si atom.
populations
(1972c) found that bond overlap
varies with differing
the basal-apical
bond lengths
basis set was used for these calculations,
In a series of calculations
is non-linearly
for tremolite
that the observed
seem to form two separate
cules, Louisnathan
correlation
EHMO calculations
and noted
of the electrostatic
the electrostatic
*Numbers
bonds
to it from
bond strength
is defined
in parentheses following amphibole names refer to structure refinements in Table A-I at the end of the chapter.
29
is
:!f
• Si-Olnb,) o Si- 0lb,)
I
1.6~ ~
• So-Olnb,)
t
rtf to
Itrf
f'''
j
t
t
j~llir~
.!, .
O~~I"t//tr.!H
~t
t
1.6~
J4! II!
1
?
oSo-Olb,)
t
1.60
S. 0-0
1.60
1.65 colc
IA)
Si-O cc!c
-
• (A)
1.65
Figure 18. Comparisonof observed 51-0 bond lengths in C2/mamphiboles (with little or no tetrahedrally coordinated Al) with values calculated according to the methods of Baur (1970, 1971). The left-hand graph shows values calculated using predicted distances and the right-hand graph shows values calculated using observed distances.
as the formal valence Deviations
of the cation divided by its coordination
of up to 40% from this rule are encountered
tures and these deviations cation-anion
distances.
bond strengths
are accompanied Several
have been developed;
1971) and Brown and Shannon Baur
bond strength
forecast
mean bond length,
comparison 18.
The agreement
method,
structure
modelling
Villiger,
1969).
struc-
variations
in
to
of Baur (1970,
Si-O bond length to the
bond lengths
deviations
and calculated
the observed
by distance
is given in Figure
This indicates
valence
least-squares
that the
rule (Baur, 1970) quite
of this scheme promises
30
A graphical
is much the same for each
A.
of 0.01
electrostatic
nature
from a
with the ob-
from that mean.
bond lengths
values
This equation_
absolutely
or it may be used in conjunction
obey the extended
and the predictive
relating
by the oxygen anion.
individual
with a grand mean deviation
amphiboles well,
with
an equation
to predict
of the observed
by antipathetic
that relate bond lengths
of these, the schemes
received
may be used both to predict
served mean bond length
in mineral
(1973) are the most general.
(1971) has derived
total Pauling
schemes
number.
methods
to be useful in
(DLS; Meier
and
Brown and Shannon bond valence.
(1973) have derived
Although
curves relating
they are not immediately
scheme of Baur (1970, 1971), they recognize are either
ignored or overemphasized
bond-strength presented
curves,
including
by Brown and Wu (1976) and Brown of a complete
taining
little or no tetrahedral
the bond-strength apparent
bond-valence
coordinating
to 0(4).
regardless
stituent bonds.
observed
This is of particular
of other variations
cation
Table 9 shows the
scheme.
It is struc-
in the bond-valence
significance
with respect
show extremely
generally and/or
con-
are compared with
in the refined
all of which
in chemistry
that
Additional
anion, have been
the results
Thus in the clinoamphiboles,
order to maintain
interactions
on eight clinoamphiboles
from ideality
the 0(4) anion,
as is the
method.
from the formal Pauling
the deviations
the anions.
to cations bonds
AI, where
that the bond length variations
sums around
(1978).
analysis
sums calculated
tures tend to minimize
weak bonding
in the previous
some for the fluorine
results
bond length to
predictive
T(2)-0(4)
structure.
short
~ 1.60
A
In
a mean bond length in accord with the size of its con(Si), there is a concomitant
lengthening
As a result of this, T(2) is generally
of the other
the more distorted
of the
two tetrahedra. Brown and Shannon mean bond lengths
(1973) and Shannon
are significantly
(1975, 1976) have shown that
correlated
n ~ = {i=l L [(1.-1 )/1 1 2 In} m m
with polyhedral
x 10
4
distortion
,
l
where
Ii = bond length,
1m = mean· bond length, n = coordination
In the non-AI IV amphiboles,
and Hawthorne
that this variation
(1976) showed
Figure 14 shows the relation amphibole
tetrahedra
tion is well developed, fecting mean culation
bond
Brown and Shannon
with
in tetrahedral
(1973) suggests
tetrahedral
the correla-
oxyanions
are not clear.
from the Si-O bond strength that any relationship
should be obscured
distortion.
Although
is not clear as the factors
Conversely,
(314) of silicate
is significantly
Baur (1978) showed
tetrahedra
31
between
afCal-
curve of mean bond
by random error in the observed
Baur (1974) has shown that IV
in a large number
A,
with ~.
mean bond length and ~ for C2/m
its significance
lengths
1.622 and 1.636
correlates
little or no AI.
of the ideal relationship
length and distortion values.
between
containing
varies between
nuIDber.
correlated that
was not significantly
o
0
N
N
0
r-.
0
1"'\
~I
0
~~~~~~~
en
C!
0;
~
~~~~ cr: ~
N
.-I
.-I
.-t
;;
ClJ
.--i
o
.n
~
;:::
0
co o '"
.....
N
N
~
.,..,
0\
.....
'"
'" \0
N
..-4
0000
CI'>
N
0
g0 ~ g0
Q)
N
gO
.
-- ~ S
..... 0 .... N
ec 0\
g: a-
~~I ~ 0
o o
c:
a-
~ r--
0; o
~!I c: c:
'M
~ :;:
ClJ .--i
ClJ
C/)
H
o
....
..;f 0\
...:t
N
"'"' .-I
.-4
~
~
.
~I~~
0\
0\
'"
a
"
o
0
0
..;f
~:~:
0 \0
NI ~
~ '"~ o
i',===~~~~
o
N
~ ~ ~ 8 ;:!. ~
..... 0'>
00'>0
o o
o
000
~
..:t \0
~:;: ~I o ...: .;.
~~ ~
N N
N
::::.
,....
~ ~ c: ~ c: ~ c:
N
000
~~ o ~ ~ ~ ~~ ~ ~ .. 10 0 " ~J ~ ~ ~~ ~
o ~ Z i
(.)
0
~~~~I ~
a-
.-4
o co
I:i
..,
~
'"
D 0 ~ M
~
o
'0 ClJ
N
g ~ ~~ g
\0
ec
;:l
I I:i
g
N
~
en
.--i oj
~
N
u
~ ~
S ;:l
~
N
~~~~~~~
0
~
..c::
(:j LI"I
E ~ ~ ~ : : ~
..,
~I N N ,...:; ~ ,...:; N N
0
N
'M
N U
.-I
000
N
........
'-'
.._,
.._,
~~~ ...............
'-'
o
0
0
0
0
0
0
0
0
,...., \D
.......
000
ClJ
.--i
~ H
o a
o.w
C!
N
0 0
0 0
r-\0
0 0
N
_
.-t
N
0 0
CX)
0
V"I
""
VI
0
N
.-I
..-4
...;
N
N
N
M
N
0
..-4
0\
N
..;f
(0
o o o
~....... ~ g ~ ::: ~ g
c: c: ": ~ ~ c: N
4" r-
c: c: c: ~ c:
0\
0 ..0
0
0
\0
""
o
\0
LI"I..:t
,...:;a 0\
c:
>.0 '"
0
a-
r-'" \0 ~
0-
..;
~~~~ 0; c: c: ~
I
e-e
N 0
'"
0
.., 0 co If)
.....
.-4
c: '";
00\0
co
N
N
o ,.....0
0
'"
0
g ~ g ~ ~ ~ g
N
N
N
c:
.-t
..........
r0
.-I
o ~
]1 8
0 0
.., ...0 0 0
N
~I
_; ....; ..;.
e-e
~ ~ ~ § o
e
-e"
~
·· · ~I~+
" ~ ~ '"o ~ :;::
I~
N
0
"
~
~ ~ o
ec
0
~ ~~~ ~ e
000
~I:::.!:;
U
0
0
!:! 0
e ~e 0
0
0
..-4
'-'
N ._.
(.!)
0
0
0.07, the A and M(4) compositions
considering
the occupancy 2+ •
to ob-
are adjusted
by
of A by K, and then the occupancy
of
M(4) by Ca, Na and Fe Ungaretti
et al. (1981) get excellent agreement between amphibole
compositions
determined
in this fashion and by electron microprobe
Compositions
determined
by x-ray methods
dispersive
spectrometer
analyses
than are the energy-dispersive
47
analysis.
are closer to the wavelength-
spectrometer
analyses.
method works
for a wide variety
It will be interesting
Amphibo1esexhibit rule (Pauling, valence
considerable
length variations
hedral
in amphiboles.
observed
cations bonds
tend to minimize
chain,
coordinating
of the other bonds cation sites.
tures.
cations,
to these cations,
This is evident
tional parameters
the deviations
cations
in the
the tetra-
with respect
show extremely
mean bond lengths
to
short
in accord with
there is a concomitant
lengthening
resulting
distorted
in extremely
from Table 16 which
for the cation polyhedra
of the M(2)-0 bond lengths
lists some distor-
in selected
amphibole
is the correlation
struc-
between
the
and the mean charge of the M(4)
(Fig. 28).
Table
16.
Polyhedron
Distortion
Pacameters
1n Selected
Crunerite(22) (26)
Tremolire(30)
C2/m Amphiboles
__!1i!l_
___.IQl__ Z a
Glaucophane
from ideality
significant
Also in accord with this argument
dispersion
bond-valence
As we saw when examining
the 0(4) anion, all of which
the size of the constituent
and thus bond-
it can be seen that the bond-length
this is particularly
In order to maintain
to 0(4).
model,
second
strong effect on bond-
Table 9 shows empirical
in which
sums around the anions.
double
from Pauling's
should have an extremely
tables for C2/m amphiboles,
bond-valence
deviations
1960) for a formal bond-valence
requirements
variations
to see how well this
of amphiboles.
a
M(2) ------2a
2
M(3)
a
2
0.29
0.8
0.78
15.8
2.25
36.0
2.79
43.2
0.11
0.05
0.6
1.88
17.4
0.21
6~.5
15.77
35.0
0.34
60.9 85.0
0.54
5.0
4.14
19.9
0.]5
35.6
5.52
22.9
0.09
43.6
0.9743.3
2.06
14.3
5.60
22'{,
0.62
43.1
1.2.54
33.1
0.38
6.2
3./,5
1s . 3
0.01
46.9
5.76
21.9
1.03
0.59
6.6
1.42
19.1
1.25
50.5
5.98
24.3
0.01
75.7
0.63
4.8
0.61
17.0
4.00
57.3
5.00
19.6
0.33
106.0
Potassian oxy-kaersutlte(55)
0.29
5.8
1.16
18.9
14.35
47.9
7.0631.2
0.05
56.8
Po r as s Lan
0.25
3.6
1.53
13.8
2.45
45.8
8.53
28.7
0.08
82.3
FIUDr-richter! Fluor-
te (34)
tremo Ii te (36) p a r g as ite (38)
Po tass ian
Fe rro- tschermaki
te
(54)
ferrl-taramite(59)
Fluor- r Lebec k t r e I 68) Fer
6 ::
co- g Laucophan¤(
f
n
>:
.
I (!l1-~
1=1
n
=
number
69)
)/Q. m
coordination
ttl
1.05
11.4
5.54
21.4
0.51
44.6
17.27
44.5
0.60
67.6
0.02
4.4
2.0Z
12.7
0.29
47.9
15.48
39.1
0.26
68.7
0.06
0.7
2.04
14.8
0.39
70.5
14.36
31.9
1.14
97.4
f ve ds on f te (67)
Potassium-ar
of
47.9
2 4 I In}xlO , where
2..
= Lnd Lv t du a I hom) length,
g_
""
mean
b on d
number of
length,
bond
mIlO
polyhedron;
bond
2
0
2
n
I. (°1-0 1=1
au g Le s 1n coordination
)
/(n-l),where
m
H. 1
poLyh ed ron .
48
t
nd
LvLdun
l
bond
angle,
0
m
'"
Lde
a
I
b
on
d
aug
I
~o
•
•
1
1.5
Figure 28. Variation in polyhedral distortion tJ. of the M(2) polyhedron as a function of the mean formal cation charge at the M(4) site in the C2/m
•
amphiboles.
After
Hawthorne
(1976).
)(
N
1,0
:l:
M(3) M(l) > M(l) > M(1) "M(2)
>
- M(2) "M(2) - M(3) ~ M(l)
M(2) M(2) M(3) M(3) M(4)
>
-
M(3) 11(4) > M(2) "M(2)
M(l) M(1) M(1) M(1) M(l) M(l) M(1) M(l) M(1) M(1) ~!(1) 11(3) M(3) M(3) M(l) M(3) M(3) M(3) M(3)
-
M(3) + M(3) - M(3) - M(3) »M(2) > M(2) - M(3) > M(2) - 11(3) > M(3) > M(3) > M(l) > ~!(1) > M(l) > M(3) > M(l) > M(1) > '1(1) > M(l)
M(2) + M(4) M(2) "M(4) M(2) ~ M(4) > M(2) > M(4) - M(3) - M(4) - M(3) "M(4) > M(2) "'1(4) > M(3) "M(4) "M(2) - M(4) "M(2) - M(4) "M(2) - M(4) "M(2) ~ '1(4) "11(4) • '1(2) > M(2) "M(4) "M(2) > M(4) "M(4) > '1(2) "M(4) > ;!(2) "M(4) > M(2) > M(4) "f!(2)
M(2) M(l) M(3)
> M(l) - M(3) • M(l)
> M(3) "M(2) "M(2)
>
X(3) > M(1) M(l) > M(3) M(l) > M(3) M(l) "M(l) M(1) > M(3) 11(1) > M(3) 11(3) > M(l)
"M(2) "M(2) "'1(2) - M(2) > M(2) "11(2) "M(2)
-
>
> >
> >
M(4) M(4) M(4)
has been made. individual
estimated
M(4) M(4) > '1(4) - ~!(3) "11(4) - M(4) - M(4)
whZ..;:e
Fe3+ an estimate
Fe
site occupan-
for the M(2) site are predominantly in the site occupancies given;
given with the combinej suggest significant Fe
In the amphiboles
>
>
>
grouE
-
0.42
M(l) M(1) M(1) M(3)
> >
-
grouD
calcic
0.15 0.85 0.il(0.85)
Alkali ( 26) (64) (65) (66) (67)' (68) ,
M(4) M(3) M(4) M(4)
"M(l) M(3) > M(4) > M(4) > M(l)
>
E;rouE
0.59 0.48 0.27 0.52 0.6 0.4 0.78 (0.84) 0.45 0.24 0.22 0.28 0.29 0.45 Sadie
( 35) (51) (59)
0.51 0.42 0.65
-
-
M(4) M(4) M(2) M(2) M(3)
-
0.35 0.58 0.24 0.32
0.59 0.35 0.42
Refinements
group
0.76 0.99 0.09 0.05
-
Calcic
(38) (39 ) (42) (44) (45) (46) (48) (49) (50) (54) (58) .* (60) (61) (70) .,
Structure
M(4)
M(3)
Iron-magnes
Crystal
Fe+Mn occupancy in parentheses. the M(l) and/or M(J) sites.
+ at
of the tirodite-dannemorite
series,
MnL+ is
at M(4); however, Mossbauer measurements show this ordering is not complete and FeZ+ also occurs at M(4). Combined Mossbauer and infrared measurements (Bancroft et al., 1967a) show FeZ+ to be at M(Z) relative
to M(l) and M(3) in tirodite.
74
2
The Fe
+
distribution
in hoilimquistite is very different
from that
exhibited
by the other Fe-Mg-Mn amphiboles. Crystal structure refinement Z shows the Fe + site preference M3 > Ml » M2 ~ M4 ~ 0.0, and this is confirmed by Mossbauer
(Law, 1973) and infrared
spectroscopy
(Wilkins
et al. ,
1970). Anthophyllites temperature
dependent
preference,
(Seifert,
but the degree of ordering
the MZ site in gedrite equally
distributed
variation
refinements
1978).
is occupied
Gedrites
is
show the same site-
is not as great. In addition, Fe2+ is approximately
by AI, whereas
among the Ml, MZ and M3 sites in anthophyllite.
Calcic amphiboles. complex
of FeZ+ at M4; this ordering
;show strong ordering
The calcic amphibole 2
in Fe
+
ordering.
group shows an extremely
The results of crystal
structure
in Table 24 where it can be seen that no exact overall pattern is apparent. However, the predominant FeZ+ ordering pattern seems to be M(l) ~ M(3) > M(Z) ~ M(4). Obviously, the FeZ+ ordering pattern
are summarized
is strongly
reasonable
dependent
on bulk composition,
to look for an overall
M(Z) is affected and Rossman
pattern.
Z+
content
of
by the trivalent
cation content of that site. Goldman Z (1977) have shown that low Fe + tremolite may show the or-
dering scheme M(4) > M(1,Z,3),
whereas
actinolites
a result of the fact that M(4) is predominantly molite.
and it may not be
Thus, the Fe
More subtle
inductive
will need more adequate
show M(1,2,3)
occupied
by Ca in tre-
effects may also be present,
experimental
> M(4),
data to characterize
but these
with any
certainty.
Bodie-calcic amphiboles. so far examined M(Z) ~ M(4).
The hydroxy-amphiboles
tend to show the site-occupancy
All of these amphiboles
pattern
show significant
of this group M(3) ~ M(l) » trivalent
cation
occupancy
of M(Z); a different pattern is expected for the richterites. Z In fluor-richterite, Fe + shows the ordering scheme M(Z) > M(l) > M(3)
> M(4); this pattern presumably results from the well-known FeZ+ for F-coordinated sites in minerals.
Alkali amphiboles.
Metamorphic
amphiboles
antipathy
of
of the glaucophane ..•
ferro-glaucophane ...magnesio-riebeckite ...riebeckite series show a Z regular Fe + distribution (Fig. 37) with the ordering pattern M(3) > M(l). This may be perturbed
by the presence
75
of Li, which preferentially
orders
~
•
c: o
. ..•. r·
Cl. :::!
_•••
o o
o
:E
Figure 37. The distribution of Fe2+ over the M(l) and M(3) sites in glaucophane . ferro- glaucophane ... magnesio-riebeckite . riebeckite amphiboles (.) and nyooLtes ( • ); from Ungaretti et al., (1978). The * indicates riebeckites of igneous origin that contain significant Li.
+ N
Q)
LL
1.0 Fe
M (3) site-occupancy
2+
at M(3) and can lead to a reversal ordering
in nyboites
is somewhat
> M(l), but FeZ+ may be strongly M(Z);
this could be clarified
of the Fe
irregular. ordered
2+.
order1ng
Generally,
pattern.
Fe
these show M(3)
into M(Z) or completely
by examination
Z+
avoid
of less magnesium-rich
varieties. Magnesium The behavior of Mg in amphiboles is generally antipathetic to that Z of Fe + and will be considered only where it is of particular crystalchemical
interest.
tonite .•.grunerite M(4) site.
In C-centered
In studies where the derived
than 1.0, the balance present.
amphiboles
may be assigned
Any significant
M(4) occupancy
and is thought
ture variant
(Papike et al., 1965, 1969).
occupancy
amphibole
Fe + occupancy
The orthorhombic
and gedrites[32]
amphibole
Witte et al. (1969), in which
and synthetic 1976).
the M(4) site is presumably
76
(Li,[])
The only other
Mg site-occupancy
NaMgNaMgsSiSOZZ(OH)Z
Mg and Na in equal proportions.
struc-
Fe-Mg-Mn
and [33] show considerable
(Maresch and Langer,
of note with regard to unusual Fe-Mg-Mn
of M(4) is less
to be the cause of this particular
anthophyllite[Z3]
thetic monoclinic
from the
by Mg occurs only in PZl/m
of M4 by Mg, as does protoamphibole[ZO]
(Li,Mg)ZMgSSiSOZl+x(OH)3_x
excluded
Z
to the small amount of Ca generally
tirodite(Z7)
amphiboles
of the magnesio-cumming-
series, Mg seems to be virtually
is the synprepared
by
occupied
by
Manganese In Fe-Mg-Mn
amphiboles,
Mn is strongly
(Bancroft
et al., 1967a; Hawthorne
amphibole
groups,
there is little
When the C-group excess
cations
Grundy,
it is consistent
studies,
although
the
and
in sodic-calcic at the M(l), M(2)
M(3) > M(l) ~ M(Z) was observed are highly
of Mn
1976; Hawthorne
to derive Mn site-preference
these results
in the trivalent
of Mn.
with the behavior
(Hawthorne,
on the basis of mean bond lengths
and M(3) sites; the preference
present
on the distribution
S.O, some studies have assigned
Some studies
1975) have attempted
and alkali amphiboles
For the remaining
in the order Mn > (Fe,Mg); there is no
direct proof of this, although amphiboles.
at the M(4) site
1977b).
information
cation sum exceeds
to the B-group
in the Fe-Mg-Mn
ordered
and Grundy,
speculative.
in both
When Mn is
state, ordering
at the M(Z) site is to be exof Al and Fe3+.
pected by analogy with the behavior Lithium Li occurs in significant although
it is capable
In the Fe-Mg-Mn significant completely
of occupying
amphiboles,
Li.
Crystal
ordered
quantities
only in certain
a wide variety
only holmquistite
structure
Analyses
of calcic amphibole 1961; Wilkins
atoms p.f.u.),
the structure.
1976), both
1963) suggest
(Knorring
spectroscopy,
and White
sites in riebeckite.
ordered
that this ordering
77
(Sundius,
in
of 1946;
cation in these amphiboles.
Addison
of a fluor-riebeckite(6S) completely
the Li occurs
constituent
considerations
that Li is a C-group
showed Li to be almost should be stressed
with holmquistite
Li can be an important
that Li occurs at the M(l) +M(3) refinement
coexisting
et al., 1970) show only small amounts of Li
and stoichiometric
On the basis of infrared
structure
(Maresch and Langer,
and there is no evidence where
Conversely,
amphiboles,
Borley,
re-
Li occurs
(together with Mg) and at the A-site.
and Hornung,
alkali
the infrared
Li also occurs in protoamphibole
[ZO] and (Li,[])(Li,Mg)ZMgSSiSOZl+x(OH)3_x
(~.16
show
show Li to be virtually
This agrees with
at the Ml + M3 sites in holmquistite.
the M4 site
of sites in amphiboles.
et al. (1970), which show that no significant
sults of Wilkins
types,
and clinoholmquistite
refinements
at the M(4) site.
amphibole
(196S) proposed
Subsequent
containing
at the M(3) site.
pattern
crystal
significant However,
is for a fluor-amphibole
Li it
[0(3) ~ 0.6F
+
0.40H] and the ordering
amphibole,
although
high Li contents
F contents
in alkali amphiboles
may be different
are generally
in a hydroxy-
associated
with high
(Lyons, 1976).
Calcium Ca is virtually
always assigned
and all x-ray studies compatible
with
this assignment,
tures so far examined.
amounts
(1976) has suggested
tain significant
amounts
during analysis
In the Fe-Mg-Mn
transmission
incipient electron
smithite,
components
amphibole
may have small
this occupancy
C-group
occupancy.
of Ca are assumed
is real or whether lamellae
studies.
assemblages,
to occu-
these amphi-
must await detailed
Certainly
exsolution
is widespread.
con-
(e.g., Li) that have been
the small amounts
microscopy
Ca occupies
only recorded
that some alkali amphiboles
calcic amphibole
Mg-Mn and calcic amphibole by the Fe-Mg-Mn
in the unit formula.
sites or that many of these amphiboles
of minor
py the M(4) site; whether boles contain
Ca is ever significantly
but would show significant
amphiboles,
appear to be
the M(4) site in all struc-
to fill the B-group
of Ca at the M(1,Z,3)
ignored
Ca occupying
in the unit formula,
amphiboles
It is not certain whether
in excess of that required Hawthorne
to the B-group
of calcic and sodic-calcic
in coexisting
Fe-
of calcic amphibole
In the rare amphibole
joe-
the two M(4) sites and the A(Z) site; this is the
amphibole
where
the A-cavity
is occupied
by a divalent
cation. Sodium Na is assigned
to the A- and B-groups
(19Z9, 1930) proposed amphibole Heritsch
structure,
of the unit formula.
Warren
that Na would occupy the M(4) and A-sites
in the
and this was confirmed
et al. (1957) by crystal-structure
crystal-structure
work has confirmed
by Whittaker
(1949) and
refinement.
All subsequent
these results.
Potassium K is always
assigned
and all experimental
to the A-group
work so far published
(Papike et al., 1969; Cameron positional
disorder
is discussed
in the amphibole is in agreement
et al., 1973b; Hawthorne,
of Na and K observed
in detail in the section
78
in crystal
on the .A-site.
formula
unit,
with this
1976).
structure
The studies
Beryllium Joesmithite
is a remarkable
T(l)B site, apparently tinct tetrahedral
amphibole
in which BeZ+ occupies
the
showing no disorder with Si over the four dis-
sites.
Boron Kohn and Comeforo
(1955) report the synthesis
of a calcic fluor-
amphibole containing considerable B3+. The chemical analysis indicates IV VI 3+ . 1.lZ Band 0.33 B p.f.u.; as B has not been recorded 1n octahedral coordination
in an oxide environment,
additional
evidence
is needed be-
fore this result can be accepted. Cobalt Z Co + occupies
the M(l), M(Z), M(3) and M(4) sites in the structure
of "NaZHZCo5SiSOZZ(OH)Z" apparently
deviates
are apparent
from its ideal composition.
from the chemical analysis
thesized
by Nesterchuk
spectra,
Chigareva
hedral
(Prewitt, 1963; Gibbs and Prewitt,
somewhat
1965), which
Similar results
of fibrous cobalt amphibole
syn-
et al. (196S).
On the basis of optical absorption et al. (1969) proposed that CoZ+ occurs in both octa-
and [Sj-fold coordination
in synthetic
cobalt fluor-richterite.
Nickel Chemical
analysis
of synthetic
1965) shows Ni to occupy
nickel richterite
(Fedoseev et al. ,
the M(l), M(Z), M(3) and M(4) sites.
Chromium On the basis of optical absorption spectra, Chigareva et al. (1969) 3 propose that Cr + occurs in [Sj-fold coordination in "chromium fluoramphibole. " Conversely, 3 for Cr +-bearing
Goldman
(1977) presents
actinolites
electronic absorption spectra that indicate Cr3+ to be in [6j-coordination.
Zinc Klein and Ito (196S) report chemical several analyses
zinc-bearing suggest
amphiboles
analyses
from Franklin,
that Zn occurs at the M(1,Z,3)
79
and physical
New Jersey. sites.
data for
The chemical
Germanium
et al. (197Z) and Grebenshchikov
Sipovskii the synthesis (OH)Z where
and characterization
Si is entirely
FACTORS Several
AFFECTING
in amphiboles
IN AMPHIBOLES
the factors affecting
(Ghose, 1965, 1977; Litvin,
cation ordering
1966; Hawthorne,
1975b), but
is far from being resolved.
In a refinement
of the crystal structure
(1949) found that the monovalent
M(4) site and the trivalent preferential
occupancy
the occupancy
of M(Z) by trivalent
of the adjacent
dicated by Whittaker ation, because
the M(4) site.
cations was explained
potential
and clinoholmquistite, this argument
cation. explain
In the case of riebeckite,
which
show a similar
as from
As inthe situ-
then arises as to why the monovalent
to result from the large size of the Na atom.
The
at M(Z) that results
this does not completely
cation
this may be assumed
However,
for holmquistite
cation charge arrangement,
cannot apply as Li is small enough to occupy the M(l),
M(Z) and/or M(3) sites, and has been shown to do so in Li-bearing
rie-
beckite
(Hawthorne, 1978c). Ghose (1965) has also cited this factor as affecting cation-ordering in amphiboles and further suggested that Fe3+ and Ti4+ may occupy the M(l) and M(3) sites in oxy-amphiboles. The effect of relative amphibole
electrostatic
structures
has been considered
(1971), who made the following (i)
potentials
Richterite
Clinoholmquistite
sites in the
in more detail by Whittaker
predictions:
has Na at A and NaCa at M(4);
for fluor-richterites(34) (ii)
at different
this is the case
and (35).
has LiZ at M(4);
this is true for clino-
holmquistite(6Z). (iii)
LiNaMg6SiSOZZF2
has Na at A, Mg at M(4) and Li at M(3).
80
,
at the
at the M(Z) site.
M(4) site by a monovalent
(1971),
the question
of magnesio-riebeckite(3)
cations were ordered
cations were ordered
from the lower electrostatic
occupies
NazMg6GeSOZ2
by Ge.
energy
Whittaker
arising
of a fibrous amphibole,
CATION ORDERING
studies have examined
as yet the problem Structure
replaced
et al. (1974) report
(iv)
Oxy-amphiboles
have a preference
valent
at M(l); this is the case for potassian
cations
for trivalent
or quadrioxy-
kaersutite(40). (v)
All amphiboles cations
(vi)
(except oxy-amphiboles)
strongly
ordered
In magnesio-hornblende ordered
at M(Z);
have trivalent
this is generally
and tschermakite,
C-type
the case.
Al is preferentially
at T(Z); this is not the case for magnesio-hornblende
(45) and ferro-tschermakite(54). (vii)
In edenite, entially
katophorite
occupied
and taramite,
T(l) should be prefer-
by AI; this is the case for potassian
ferri-taramite(59). Bond-valence The effect of local charge balance amphiboles concluded
with occupied that tetrahedral
(1978b) has considered the cation ordering importance
rule
in amphiboles.
a particular
stoichiometry
stoichiometry.
Miscellaneous
factors reasonable
of cation ordering
success
in amphiboles
only apply to the relative formal valences. sophistication)
Calculation
should
of the mean
with Pauling's
second
consonant
shows the arrangement
with
with the
cation arrangement
has been achieved
for
in the rationalization
by energy and bond-valence
ordering
on
and their relationships
charge arrangements
to be the preferred
that specific
Hawthorne
requirements
that the same mechanism
from exact agreement
R.M.S. deviation
Although
requirements
suggesting
1960) for all possible
amphibole
(1965) who
Recent work has shown the
on cation ordering.
(R.M.S.) deviation
(Pauling,
smallest
patterns
controls
anions in
by Ghose
Al should order into the T(l) site.
in bond length,
exert stringent
around the bridging
has been examined
the effect of local bond-valence
of local bond-valence
to variation
square
A-sites
methods,
these
of cation species with different
They do not apply (at least at the present level of to Al/Fe3+ and Mg/FeZ+/Mn ordering, and an appeal to
other criteria must be made. that may influence
ordering
Ghose
(1977) has reviewed
in amphiboles:
81
several
factors
Ionic size.
Ghose
(1965) suggested
in the site-occupancy
of the M(4) site.
monoclinic
can accept
amphiboles
site in the orthorhombic cations.
distribution
Strongly polarizing
cations.
that size plays a role in the
Strongly
Strongly
In addition,
the octahedral
polarizing
cations
like
bonds with oxygen and hence will prefer
the M(4) site (Ghose, 1961, 196Z).
tend to distort
[6J-fold
Al in gedrites.
FeZ+ tend to form more covalent
tend to avoid each other.
the smaller
can accept only FeZ+, Mg and smaller
(1970) suggest
of tetrahedral
[SJ-fold site in the
Ca and Na, whereas
amphiboles
Papike and Ross
that this factor plays a role
The large
polarizing
strongly
cations will
polarizing
cations will
sheet and hence will be repelled
from the
M(l) and M(3) sites, in accord with the fact that in orthopyroxeneZ cummingtonite assemblages, orthopyroxenes are more Fe + rich than the coexisting
cummingtonite.
Relief of Si-O-Si bond strain. tetrahedral
Devore
(1957) suggested
that
Al is more likely
to order into the T(l) site, as the occupation of this position by Al causes fewer Si4+ cations to share more than two anions with other Si4+ cations, hence relieving the Si-O-Si bond strain.
Steric considerations. (1965) proposed an anticlockwise into T(l) will
When M(4) is occupied
by Ca or Na, Ghose
that the 0(4) atoms recoil away from the M(4) site causing rotation
of the T(Z) tetrahedron;
cause T(l) to rotate clockwise
substitution
to compensate
of Al
for this
rotation. Certain
remarks
posed above. patterns
are in order concerning
Firstly,
is of use only in exaggerated
cation radius polyhedron
(e.g., Ca and Mg) occur.
of a cation adjusts
and its size is irrelevant with the exception
some of the mechanisms
the use of ionic size to forecast cases where In general,
to accommodate
to the possible
that the normal
gross differences
cation,
of other cations
radius ratio rules will probably
With regard
to the possible
does prefer
the M(4) site in the Fe-Mg-Mn
effect of highly
polarizing
amphiboles
in
the coordination
its constituent
occupancy
pro-
site-ordering
cations,
Fe
apply. Z+
(Ghose, 1961; Finger,
1967, 1969, 1970) and in tremolite
(Goldman and Rossman,
MnZ+ has an even higher preference
for the M(4) site (Bancroft et al. ,
82
1977).
However,
1967b; Hawthorne
and Grundy,
1977b) that is not in accord with this
mechanism.
In addition,
each other,
then there should be a lack of clustering
in the structure.
if strongly
Except
polarizing
cations
tend to avoid of Fe2+ cations
for the cummingtonite-grunerite
series,
this
is not in accord with
the infrared results of Strens (1966) which indiZ clustering of Fe + (and Mg) in holmquistite, glauco-
cate significant phane,
riebeckite,
Crystal
tremolite
and anthophyllite.
field stabilizat.ion energy
In the free ion or in a spherically-symmetric 3d-orbitals
are energetically
of lower symmetry
removes
levels as the reducible
degenerate.
the complete
potential
Application
degeneracy
representation
field, the
of a potential
of the orbital
field
energy
spanned by these orbitals
must
contain
the irreducible representations of the symmetry group. HighZ 6 spin Fe + has a d configuration, and thus the lowest energy 3d-orbital is occupied
by two electrons.
As the average
is equal to the energy of the degenerate spherically-symmetric
crystal
of the undegenerate
field stabilization
will tend to occupy Several neighbor
energy
levels and enhance
affect
term.
C.F.S.E. with nearest-
that the bonded field.
will produce
anions reflect
According
a greater
providing
to this ar-
splitting
of the
that the "bond type"
in each coordination polyhedron. The agreement is not Z good; Fe + is often enriched at the M(l) and M(3) sites as
compared with
the predicted
factors
the effects
C.F.S.E.
to correlate
the C.F.S.E.,
the sta-
the orbital term, and hence FeZ+
the C.F.S.E.
of the crystal
distortion
this value
and is known as the crystal
on the assumption
and symmetry
increased
particularly
stood.
the greater
between
thus enhances
Thus, the greater
the site with the largest
configuration
is identical
several
(C.F.S.E.).
studies have attempted
the strength gument,
3d-orbital
configuration
energy
energy level splitting,
levels in a corresponding
field, the difference
and the energy of the lowest energy bility
energy of the five orbitals
of polyhedron
Variation
enrichment
that are pertinent distortion
in individual
the magnitude
the effect of varying
at the M(Z) site.
There are
to the use of this criteron. on the C.F.S.E.
are not well under-
bond lengths and variation
of the orbital bond angles
splitting.
in bond angles
Some studies
in a simple systematic
83
Firstly,
way
have examined (Krishnamurthy
and Schaap, relative
1970; Garner and Mabbs,
orbital
energy levels are considerably
effect of variation bond length) irregular
in individual
pseudo-octahedral
gross differences
in an octahedral
local environment
Thirdly,
in the crystal,
affect the orbital figuration
of the coordination
unless that structure
Ribbe and Gibbs a function
series
exhibited
on the as char-
is not strictly
that the C.F.S.E.
that Dq (a measure
con-
may also be
of the orbital
split-
field) decreases
Z Fe +X
6
will tend to avoid sites coordinated populations
splitting
environment
in a structure Z is an Fe + end member.
for octahedrally-coordinated
ment is supported
This
Thus, using the average
(1971) have suggested
crystal
the magniions.
is dependent
polyhedra
of anion type, noting
ting in an octahedral
unless
and this may also significantly
(Das, 1965).
applicable
with
effect on orbital
the C.F.S.E.
not on the average
studies,
splitting
neighbor
The
mean
(1967, 1970), who concluded
ions have a considerable
by crystallographic
difficult
factor that may influence
the
of two
is the more irregular is extremely
by Jager and Perthel
environment.
by this.
(with a constant
is the effect of next-nearest
factor has been examined that non-coordination
coordinations
Another
bond length;
Thus, deciding which
the larger C.F.S.E.
occur.
tude of the C.F.S.E.
affected
bond lengths
is not well characterized.
regard to estimating
acterized
1970) with constant
along the spectrochemical Z groups. Consequently, Fe +
by F, as suggested
by the fluor-richterites(34)
by data for micas
(Rosenburg
by the site-
and (35).
This argu-
and Foit, 1977) and humites
(Ribbe and Gibbs, 1971). The C.F.S.E. methods,
predicts
method,
as with
ordering
energy, with
the assumption
terms remain
constant
General
energy and site-potential
that the remainder
and thus do not contribute
of the structure
energy
to the ordering
process.
considerations
The ordering affected
the Madelung
on the basis of part of the total structure
pattern
assumed by a specific
by other cations in the structure.
shows a site-occupancy shows a site-occupancy has strongly
affected
Thus in cummingtonite,
arrangement
M(4) > M(1,Z,3).
arrangement
M(1,Z,3)
the ordering
pattern
this effect is automatically bole names;
cation can be strongly
for example,
acknowledged
In tirodite,
Z Fe + Z Fe +
> M(4); the presence of MnZ+ Z of Fe +. In extreme cases,
by the use of separate amphiZ does not show the same Fe + ordering
glaucophane
84
c
o
~ ~
.Q
..>
I
984 982
.>
0 0
•
528 526
c
5.28 526
ics o
1 OJ.
-- 0_ -
__
.__
0
0-0-
_0
.C1'O'O'
,.... 0'
t~:::::::::: ... ~
6
o
.c
..r:::.
-~~
.c
s:
~n~
~ ~
.. ~~~~~~;~; ... ...·· -_. ~ ~· , 3 ~~~~~~
"0
• -'
-'
-'
_
I""l'-''-'_
~ ~~~~~~ ~~ 0"
......1"'1
................
"
o c
'-''-'
(i.I
Q)
(L)
Q)
~ c
c
t:
I:
c
~
10
Na2Mg3A12SiS022(OH)2 Ca Hg Si O 2 s
Ca2Mg2Si4012
[diJ
NaHg A1SI 0 3 3 10
(OH)2
[npJ
+
Ca2Hg2Si4012
[diJ
+
NaCa2MgsA1Si7022(OH)2
KMg A1SI 0 3 3 10
(OH)2
[ph ]
+
Ca2Mg2S14012
[dlJ
+
KCa2MgsAISI7022
s n
+ 3. S4
[ahJ
+
(OH)2
amph.)
[glJ [trJ
(OH)2
•
3.77
+ 4.SS [etJ
- 2.42
[k-etJ
- 2. 8S
Figure 8. (a) through (f) are composition planes defined by CaMgSiZ06-(Di) and the mica endmembers Mg3(Si401O) (OR)2-(Tc). KMg3(AlSi3010) (OR)2-(Ph). NaMg3(AlSi301O) (OH)2-(Na-Ph). and CaMg3(Al2Si201O) (OR)2-(CI). These include the stable amphibole end-members Ca2MgS(Si8022) (OH) 2(Tr). NaCa2Mgs (AlSi 7022) (OH) 2- (Ed). Na2eaMgS (Si8022) (OH) 2-(Ri). and KNaeaMgS (Si8022) (OR) 2- (K-Ri) • and the metastable ones Kea2MgS (AlSi 7022) (OH) 2- (K-Ed) and Ca)Mgs (A12Si6022) (OH) 2-(Ca-Ed) • Lightly stippled areas are inaccessible to biopyriboles. (g) shows phases coexisting with diopside in the system that may be defined by D1, Ph, Na-Ph, and Cl. Darker stippling shows fields of amphiboles and micas that coexist with diopside. Micas appear when the amphibole is metastable relative to the mica-pyroxene pair.
152
either pyroxene
or mica, for example.
sidered
reactions
several
phyllite
and talc.
or jimthompsonite talc, however,
In the absence
Veblen
and Buseck
chesterite
is ever stable relative
to anthophyllite
systems,
may be surprised
as indicated
by the inclusion
1976; Keusen and Peters,
1981) and by direct
synthesis
1976).
Similar
synthesis
phiboles
Natural
materials
potassium,
phibole, calcium
clintonite
with high contents under normal pair.
however,
by Hinrichsen
As pointed
to a high-alumina and
(or phlogopites)
and
form hydrates
have also appeared
of pyroxenes indicate,
of potassium
geologic
joesmithite,
by Moore
at am-
1979),
sodic micas that hydrated with biotite
on
or phlogopite 8, that am-
in their A-sites
relative
by Huebner
are
to the correspond-
the A-site
(1977), and the unusual
described
in many attempts
1974a; Greenwood,
or calcium
in which
have been synthesized
may simply be altered
as shown in Figure
conditions,
Amphiboles
and Schurmann
out by Carman, many
or montmorillonite
and may represent
occurrences
with
ing pyroxene-mica
1975; Franz
A-site vacancies
sodic-biotites
(Ernst, 1961, 1968; Carman,
cornmonly with a pyroxene,
metastable,
(Keusen, 1972;
and high H20-activities. This smectitic behavior may or hydrothermal alteration and is probably responsible
of sodic vermiculite
and of diopside
occurrences.
and Wones,
(1974b) found that at least some sodic micas
sodic micas.
in
et al., 1980; Spear et al.,
has abundant
between
in part for the rarity of these micas.
quenching.
occurrence
range from Na-phlogopite
The form wonesite
at low temperatures
phibole
and
of sodic trioctahedral
1980; Schreyer
intermediate
occur in weathering
occurrences
the phase relations
(Carman, 1974b; Hewitt
Compositions
form, preiswerkite. is thus chemically Carman
chesterite
or enstatite
by known natural
micas, but these are now known both from natural
talc.
that either
such as those of Table 3 as the
of Figure 8 show, schematically,
the simple biopyribole
and Althaus,
to antho-
interest.
The diagrams
Kulke,
(1979) have con-
and jimthompsonite
of clear evidence
we are left with equations
ones of principal
Some readers
relating
is filled by
and Papike
(1970) and
beryllium-bearing
(1969) has A-sites
occupied
amby
and even some lead!
It is clear from the volume tal volume
of a polysomatic
simply the linear
sum
data in Tables
mineral
3 and 4 that the
such as amphibole
of the volumes
153
of its isolated
to-
can not be taken as component
parts,
although the differences are comparatively small relative to those associated with many other heterogeneous reactions.
The volumetric strains,
and anticipated differences in other thermodynamic properties, can undoubtedly be related to the mismatches at the modular junctions.
It is
interesting that the ~V's of dissociation appear to be consistently negative for amphiboles with vacant A-sites and consistently positive for amphiboles with occupied A-sites, at least as measured at room temperature and one atmosphere.
This makes crystallochemical Unit
TABLE 4.
A.
1
Pyroxenes
4XM94S14012
a
5
in
cell
p
18.236
[en]
dimensions
of
sense, in that the volumes
biopyriboles.
b
c
8.821
5.182
-a
400.64
(2 )
439.62
(3)
8.979
8.563
2xCa2M92Si4012
[di]
9.378
8.931
5.249
2.663
b
a
c cos
C
4XM93SI4010(OH)2
ftc,
20]
2XM93SI4010(OH)2
ftc,
1M]
2xNaM93A1Si3010(OH)2
[np)
2xKH93AISI3010(OH)2
C.
[ph]
Amphlboles3
2xCa2H95S180ZZ
[gl]
(OH)2
[tr)
2xNaCa2H95A1Si70ZZ(OH)2
ret]
2xKca2M95A1SJ70ZZ
[k-et]
Monoclinic Molar
3.
Monoclinic
J3
(OH)2
forms
E.
forms
of
V
(A\'l
to
talc
referred
Ref (1)
9.145
5.252
°
899.17
9.36
9.145
5.252
1. 751
449.59
(1)
9.903
9.203
5.265
1.348
479.82
(4)
10.156
9.203
5.317
1.776
496.95
(5)
c
a cos
Jl
b 18.01
5.24
.p
V
°
(A')
Ref. (1)
1756.27
9.23
17.67
5.29
3.040
862.74
(6)
9.519
18.054
5.268
2.803
905.33
(7)
9.562
17.951
5.310
2.701
911.41
(8)
927.
referred
volume, ~ and
p
18.72
18.61
2xNa2H93A12SI8022(OH)2
1.
in
a sin
4xH97S i 8022 (OH) 2 [ah]
2.
5
'C-centered assumed
cells.
independent
to I-centered
(±)
of
£ cos
polytype.
a
for
1M form
assumed
to
be Y3.
cells.
REFERENCES (1)
Greenwood,
(5)
Hewitt,
1963;
1975
(2)
(6)
Frondel Borg,
and Klein,
1967;
Ref,
2.843
[jd]
2
(II')
(1)
°
2xNa2A12S14012
Micas
V
833.58
5.211
B.
p
cos
1965;
(7) Colville
~
(3) ~.,
154
Turnock
~
1966;
(8)
~.,
1973;
Hinrichsen
(4)
Carman,
1974b;
and Schurmann,
1977.
(8)
of the A-sites
may vary freely in a mica, depending
but are constrained or other hydrous sibility hence,
by the cross-linkage
pyribole.
in the direction
it is probable
of dissociation phibole
normal
destabilized
tions of Table glaucophane,
systems
by increasing
data in Table 3.
yet precisely the enthalpy
located,
End-member
(1979), inasmuch cell parameters
1966; Widmark,
1970; Gilbert by
1979; Gilbert
are consistent
all these univariant
with
curves are not indicating
that
has been questioned
a (probably metastable) of his runs produced
diopside
1) on two intermediate
(for which
edenite" with by Hinrichsen
of Na-K edenites
K-edenite.
to the diopside
The decomposition
tremolites
was synthesized
that under some conditions
authors
by Greenwood
As reported
are
all necessary
the expected and Schurmann,
and pargasites, by Greenwood
and a "soda montmorillonite,"
end-member
The unit-
et aZ. (1966), moreover,
An "end-member
a variety
by several
in the run-products.
of Colville
like those of synthetic
however,
as synthesized
1974; Peto, 1976), but the identification
as other phases occurred of the edenite
were present).
cell-parameters,
phlogopite
aZ.,
have the same signs as the volume
as true edenites
who also synthesized
relative
at high pressures
1974a, as summarized
These dissociations
edenite has been reported
aZ.,
of these amphiboles
ingredients
The amphiboles
all dissociate
(as is usual).
(Colville et
suspiciously
equilibria.
given, the equa-
1979; Day and Halbach,
differences
stabilized
pressure.
the slopes appear to be positive,
and entropy
differences
~V's
by increasing
will be initially
1974; Carman,
Although
1978);
of the
imply that am-
1963, 1971; Essene et
and Autio,
et aZ., Chapter 9, Volume 9B).
aZZ
to the formulas
univariant
and Troll,
1977; Chernosky
the volume
components
(Greenwood,
and Popp, 1973; Gilbert
(Hazen and Finger,
high pressures
and anthophyllite
into talc and pyroxene
high compres-
will be destabilized
corresponding
3 may represent
tremolite,
in an amphibole
These considerations
with vacant A-sites
In the simple
on their occupancy,
the beams
an unusually
to the cleavage
that at sufficiently
and that other amphibole
and subsequently
Maresch,
also exhibit
may become negative.
components
pressure,
Micas
between
as well as
(1979), many indicating
edenite may indeed be metastable
and Na-phlogopite.
experiments
of Hinrichsen
Na-K edenites
among the decomposition
invariably
products.
155
and Schurmann yielded
(1977, Fig.
diopside
Also present
and
in some runs
were nepheline, phlogopite.
and forsterite,
Their curves
of edenite, pleths
enstatite
diopside,
are not equilibrium
and phlogopite
on the composition
phlogopite,
would
presumably
boundaries,
coexisting
8d, will have positive
range 0-5 kbar, such that increasingly pressure
K-rich
by the univariant
curves
(001), however,
these same isopleths
pressures.
and Wyllie
sures less than 15 kbar the kaersutite positive
slope,
At pressures negative
to an assemblage
slope.
Similar
results
by Merrill
1975, summarized
earlier work;
Boettcher,
1978; and Gilbert
results).
These studies
positions
of amphiboles
and trioctahedral
in Figure
9, as should
of
and clinopyroxene.
with generalized (Merrill
of
mafic and
see Allen et aZ., 1975; Allen and
et aZ., Chapter 9, Volume 9B, for more recent
imply,
pyroxenes
At pres-
along a boundary
(1975) and others
to
by the ex-
along a boundary
occurs
have been obtained
and Wyllie
kaersutite.
phlogopite
above 20 kbar the same phenomenon
rock compositions Wyllie,
decomposes,
that includes
normal
again at much
is, in fact, reinforced
(1975) on a natural
of isopleths
for the pure Na- and
of phlogopite
may well be encountered
This last conjecture
of Merrill
and
at least in the
Such a bundle
Owing to the high compressibility
periments
that iso-
diopside
edenites will be stabilized
K-end·members.
higher
of Na-
but the presence
with
slopes,
at any given temperature.
be bounded
products
along them s·trongly implies
of the edenite
as in Figure
by increasing
the dehydration
having
collectively,
that isopleths
filled A-sites,
micas,
and that coexist with
should have the general
the univariant
curves
on the com-
form as in curve D
for the limiting
end~.member
reactions.
POLYTYPE Clinopyriboles most abundant. pyroxene,
of the simplest
STABILITY
polytype
(0)
are overwhelmingly
In these there is a large cation site designated
or M4 in amphibole
(we shall here call it Mlc),
as M2 in
that is occupied
in the more cornmon forms by Ca, less cornmonly by Na, Mg, Fe, or Mn. (ox)
and proto-
(x)
pyriboles,
the
on the other hand, are virtually
Or tho-
limited
forms in which the Mlc sites are occupied largely by the smaller species 2 2 Mg and Fe +. If Mg-Fe + or tho- or protopyriboles coexist with an Mg-Fe clinopyribole,
the clinopyribole
Mlc for Ca or Na in orthopyriboles
is the richer
in Fe.
is very limited,
156
The tolerance
of
and in protopyriboles
to
cpx • bio
J.~l __
3Oi-/--hbl-
t
-
20
P(kbl
I
I I
10
-T(OCl-
Figure 9. Association-dissociation reactions relating amphibole to mica and pyroxene. (a) and (b) are from Gilbert (Chapt.e r 9, Volume 9B); (c) is from Day and Halbach (1979). The dotted curve (d) shows, schematically, a possible form for univariant curves for end-memberamphiboles with occupied A-sites, or 150pleths on amphibole compositions in generalized 3-phase assemblages. Cd) is consistent with the observations of Merrill and Wyllie (1975), Hinrichsen and Schtirmann (1977), and other experiments summarized by Gilbert (this volume); the high-temperature segment is probably metastable due to melting in most instances.
is even less (Longhi and Boudreau, cross-modules
are strongly
1980, Fig. 2).
favored,
It is thus clear that
other things equal, by small species
(especially
Mg) in Mlc, even though the crystallochemical
are complex
(see Hawthorne,
position
MgSi03
at least
(0)
Chapter
1, this volume).
reasons
Pyroxenes
show all three forms, and those of composition
and (ox).
The experimental
for this
of the comFeSi0
results on their relative
show 3 stabi-
lities have been surnmarized in Volume
7 of this series by Lindsley
Figs. 2 and 3).
is consistent with the 3 and entropy all increase as the
generalization proportion reasons
The phase diagram that volume,
of cross-modules
for MgSi0
enthalpy, increases,
for this are, again, complex.
although
This writer
is inclined
by Lindsley
(1965), were protopyroxenes
the crystallochemical
The diagram
in that there is a second, high-temperature to believe
(1980,
for FeSi0
is puzzling 3 field for the clinopyroxene.
that these clinopyroxenes,
157
that inverted
as suggested
to clinopyroxenes
on
quenching
and agrees with Lindsley's
pyroxenoid
later
Fs-III is not a quenching
(1980) conclusion
that the
product.
Both clino- and ortho- forms appear among the Ca-poor Mg-Fe boles,
but the phase relations
1979).
Only the Fe end member
are still poorly known appears
amphi-
(Cameron and Papike,
to have both forms occurring
naturally. Certain
clinopyriboles,
again those low in Ca or Na, have primitive
(P21/c, pyroxene
and P21/m, amphibole) rather than centered cells at low The inversions to centered forms have many of the charac-
temperatures. teristics
of lambda-transformations,
as first-order. the tetrahedra (Thompson,
The primitive
cell appears
that makes successive
of the symbols
to the polytype
formula.
The primitive-to-centered
transformation
tent
Inversion
(from >llOO°C
small amounts
(1976).
temperatures
to RC> =8=
RZR ~~~
~~8~8A ~~~~~:
~~~
B~~~8
Olm
Jt
C~
~=~ ~ ~~~ ~=~
EC>Z E ~=~ ~ IEZE ~~~ 1 E'C7E ~'=7~ Cp.
Clm
b=9A
b=f8A
A
~=~==:7~: ~=~=~ ~ ~ ~~~~~ ~=~~~
~=--=7~
Cit
Cc~
b= 27A
b=45A
Figure 5. The orthopyriboles, top, all have the I-beam stacking sequence ++-- and a :: l8A (Opx - orthopyroxene, Oam z ortho~mphibole, Jt • jimthompsonite, Ch - chesterite). The clinopyriboles, bottom, have all of their I-beams oriented in the same way and a - 9A (Cpx • clinopyroxene, Cam - clinoamphibole, Cjt ~ clinojimthompsonite, Cch = monoclinic analog of chesterite). From left to right, the pyriboles are divided according to the widths of their silicate chains, which also determine t.he lengths of the b-axes, as shown: pyroxenes have single chains, amphiboles double chains, jimthompsonite triple chains, and chesterite alternating double and triple chains. (After Veblen et al., 1977.)
on the bottom
of Figure
(which is equivalent
5 have the stacking
sequence
... 1
to ..•-------- •.• ); these structures
and are called clinopyriboles.
The ordered pyriboles
divided
of the silicate
according
in Figure amphiboles
to the widths
5, orthopyroxenes
and clinopyroxenes
and clinoamphiboles
clinojimthompsonite
The diagrams
structures,
are parallel
to the silicate
is parallel
is about l8A for orthopyriboles
multiples
27A in triple-chain
Thus, as shown chains, orthoand
and its monoclinic
to the unit cell in Table 1. chains;
The c-
the length
and is about 5tA for all of
to the stacking
direction
and about 9A for clinopyriboles,
and as
Figure 5 and Table 1 also show that the lengths
depend on the widths
mate integral
as presented
by the chain periodicity The a-axis
shown in Table 1. the b-axes
and chesterite
of Figure 5 can easily be related
of c is determined the structures.
chains.
have single
double and triple chains.
of the various
axes of all pyriboles
are monoclinic
are further
have double chains, jimthompsonite
have triple chains,
analog have alternating
parameters
1 1 1 1 1 1 I •••
of 9A:
pyriboles,
of the silicate
chains and are approxi-
about 9A in pyroxenes, and 45A in pyriboles
195
of
l8A in amphiboles,
with alternating
'",..
....
'"
....
,..'"
CI)
0;:l
0 ,_, IlO Q)
H
OJ
.....e
'"
.c
... ..... ,.. OJ
'"
OJ ...
U I "tl U OJ ....
< ",,,,
'" ... ~I "il~.... s:u'" N 0-
,..
...'" '" ~; "''" ...v ,.. ,.." '" ...sn
OJ co " ...
0'I...:t-n,...,
--
'"
:::>
13
u s: '"
"tl OJ
oxenes~ Hineral. Soc.
M. and J. J. Papike (1980) Crystal Ed , , Pyroxenes~ Mineral. Soc. Amer.
Champness,
lnst.
Wash.
High resolution
P. E., G. Cliff and G. W. Lorimer scopy, lOB, 231-249.
Year
electron
(1976)
Book,
imperfecti6n
65,
microscopy
Subsolidus Amer. Revs.
chemistry Revs. in
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of silicate Mineral., 7,
285-290. of
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silicates.
Amer.
In C. T.
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In C. T. Prewitt,
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J. Micro-
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E.
(1973)
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(1975) Crystallographic Eds., Surface and
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fibrous
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Cressey,
B. A., J. L. Hutchisort asbestiform gruneri te
Dorling,
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Dyson,
S.
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G. V. (1969) 101-109.
Gittos,
475-483.
126-151.
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Crystal
structure
P.
V. E. 19,
cal-
Khadzhi and A. L. Dmitrik (1974) 1186-1193 (transl. Sov. Phys.
New
(1976) Formation conditions and physico-chemical constitution of with (Si60l6) radical (in Russian). Izvestiya Akad. Nauk., Ser.
The crystal
W. C. Forbes and P. magnesio-richterite Gibbs,
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and J. M. Thomas,
Zussman (1980) Comparitive studies of asbestiform and non-asbestiform amphiboles. Fourth Int'l Conf. on Asbestos, Torino, 317-333.
(1967)
L. W. (1970) Refinement of the Wash. Year Book, 68, 283-288.
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Sci.,
and E. J. W. Whittaker (1981) Morphology and alteration and anthophylli te. Mineral. Mag., in press.
B. F., T. Anthony and D. Turnbull App1. Phys., 3B, 3408.
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in Metals
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J. W. Oxford.
Drits,
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silicate
Christian,
J.
(1965)
defects shear
crystal
of
Interstitial
structure
structure
of
cumrningtonite.
Phakey (1974) Unmixing and magnesio-riebeckite.
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of
copper
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Acta
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tin.
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M. F., G. W. Lorimer and P. E. Champness (1976) The phase distributions in some exso1ved amphiboles. In H.-R. Wenk, P. E. Champnes s , J. M. Christie, J. M. Cowley, A. H. Heuer, G. Thomas and N. J. Tighe, Eds., Electron Microscopy in Mineralogy, p . 238-247, Springer-Verlag, Heidelberg.
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im Kristianiagebiet.
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D. A., L. G. Mallinson, other unusual faults in
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(1911)
Petrographic
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1.
Skrifter.
High resolution electron Acta Crys t.a Ll.og r . , A31,
, D. A. Jefferson, L. G. Mallinson and J. M. Thomas (1976) nephrite jade: an. electron microscope study. Mater. Jefferson,
Vidensk.
micros794-80l.
Structural Lr regu l ar Lt Les in Res. BuLl , , 11, 1557-1562.
J. L. Hutchison and J. M. Thomas (1978) Multiple-chain amphiboles. Contrib. Mineral. Petrol., 66, 1-4. terms
for
field
use.
J.
CeoL,
19,
317-322.
(1965) tiber die kristallstruktur von Ba2Si308, Naturwissenschaften, 18, 512-513.
(1980) Classification of silicates. Soc. Amer. Revs. in Mineral., 5, 1-24.
In P. H. Ribbe,
Ed.,
ein
silikat
Or-thosilicates,
mit
Mineral.
L. G. (1980) Termination of planar defects in the amphibole mineral nephrite by high-resolution electron microscopy. Acta Crystallogr., A36, 378-381.
J. L. Hutchison, D. A. Jefferson silicates by high resolution 9l0-9l1.
and
observed
and J. M. Thomas (1977) Discovery of new types of chain el ectron microscopy. J. Chem. Soc. London Chem. Commun. ~
235
, D. A. Jefferson, J. M. Thomas and J. L. Hutchison (1980) nephrite: experimental and computational evidence for chain silicates within an amphibole host. Phil. Trans. Martin,
R. F.
Nakajima,
and G. Donnay
(1972)
Hydroxyl
Y. and P. H. Ribbe (1980) clays and other biopyriboles.
in
the
mantle.
Alteration of pyroxenes N. .Ib . Mineral. Mh.•
The internal structure of the coexistence of multipleRoyal Soc. London, 295, 537-552.
Amer. Mineral.}
57,
from Hokkaido, 6, 258-268.
Japan,
554-570. to amphibole,
Nissen,
H.-U., R. Wessicken, C. F. Woensdregt and H. R. Pfeifer (1979) Disordered intermediates between jimthompsonite and anthophyllite from the Swiss Alps. In T. Mulvey, Ed , , El-ectron Microscopy and Analysis, 1979 (EMAG'79) Ens t , of Physics (Bristol) Conf. Ser , , 52, 99-100.
Papike,
J.
J., C. T. Prewitt, and ideal topologies.
--'
and M. Ross butions.
--'
------on
Peterson,
N. L.
Sueno and M. Cameron Z. Kristallogr., 138,
(1970) Gedrites: Amer . Mineral. 55,
and J. R. Clark five new structure (1968)
Solid
S.
State
(1973) Pyroxenes: 254-273.
crystal structures 1945-1972.
(1969) Crystal-chemical refinements. Mineral.
and intracrystalline
characterization Soc. Amer. Spec.
Academic
v.
Smith,
P.
P. K. (1977) An electron microscopic Mineral. Petrol., 59, 317-322.
study
Sueno,
S.,
M. Cameron and C. T. Prewitt (1976) chemistry. Amer. Mineral., 61, 38-53.
Orthoferrosilite:
Crystal structure and stability of the and phase rela tions of Mg,Fe pyroxenes.
H., S. silicate
Thompson,
J. B., Jr. (1970) pyriboles (abstr.)
(1978) Veblen,
Shimada and T. Sudo NazMg4Si6016(OH)Z.
Biopyriboles
Structural
Geometrical possibilities for AIDer. Mineral., 55, 292-293.
disorder
in
series.
synthetic
of clinoamphiboles Pap , , 2, 117-136.
lamellae
high-temperature
amphibole
Amer. Mineral.,
63,
(1976) Biopyribo1es from Chester, .Geol. Soc. Amer. Abstracts with
(abstr.)
I.
(1978a) Amer. Mineral.,
New biopyriboles 63, 1000-1009.
and
(1978b) j imthompsonite, Amer. Mineral.,
New biopyriboles from Chester. Vennont: II. clinoj imthompsoni te , and chesteri te, and the 63, 1053-1073.
and Science, and 65,
growth
(1979a)
Chain-width
(1979b) Serpentine 206, 1398-1400.
(1980) 599-623.
and
minerals:
Microstructures
(1981) Hydrous microstructures
order
and reaction
in
E. J. W., B. A. Cressey and J. Lame.lLae in grunerite asbestos.
Yamaguchi,
Y., J. Akai and K. Tomita lherzolite from Alpe Arami, 263-270.
mechanisms
silicates:
sheet
Tullis (1980) Amer. Abstracts
silicates,
and
intermediate VT. (abstr.)
mineralogy.
The crystal chemistry of amphibole-mica reaction.
biopyriboles.
in
pro-
Descriptive
Amer. Mineral.,
structures.
biopyribo1es.
Amer. Mineral.,
and uralites: 66, in press.
New minerals
in C:t>ystals.
diffusion 553.
inter-
and structural
John Wiley
and
of mul.t fp Le-cha tn
lamellae in diopside Contrib. Mineral.
Dislocation-assisted with Programs, 12, 236
chain
silicates
L. Hutchison (1981) Terminations Mineral. Mag., 44, 27-35.
(1978) Clinoamphibole Bellinzona, Switzerland.
a triple
Model bio-
and new combination
PoZymorphism and PoZytypism
Whittaker,
J
and disorder
chain
crystal
mixed-chain
pyriboles and sheet silicates in pyroxenes and reac tion mechanisms. Amer. Mineral.,
A. R. and P. Krishna (1966) Sons, Enc , , New York.
Yund, R. A. B. M. Smith and J. (abstr.). Geol. Soc.
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intergrowths
and C. W. Burnham (1977) Asbestiform groups. Science, 198, 359-365.
--' Verma,
The first 8, 1153.
and
and P. R. Buseck 64, 687-700.
Contrib.
In preparation.
Vermont: Programs,
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intergrown 1075-1086.
anthophyllites.
of
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and C. W. Burnham (1975) Triple-chain biopyriboles: Newly discovered ducts of the retrograde anthophyllite-talc transformation, Chester, Trans. Amer. Geophys. Union (EOS), 56, 1076. and
based
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and crystal structure Petrol., 66, 149-156.
D. R. (1980) Anthophyllite asbestos: microstructures, mechanisms of fiber formation. Amer. Mineral., 65, (1982)
distri-
MgSi03 polymorphs: physical Mineral. Soc. Amer. Spec. Pap , ,
of amphibole
(1978) Synthesis Contrib. Mineral.
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D. Turnbull, and H. Ehrenreich, Press, New York.
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comparisons
of garnet Pe t ro L, , 66,
of oxygen
in
albite
5
Chapter
AMPHIBOLE
ASBESTOS
MINERALOGY
Tibor Zoltai INTRODUCTION Asbestos is because
is one of the most desirable
it possesses
such as long fibrous and electric durability, desirable
and relative
for a highly
trial processes.
The corresponding
erties of asbestos.
habit.
tration
of asbestos,
or quantity
sufficient
possess
but exist only in shorter asbestos.
exploitation.
all the properties
palygorskite
minerals
which
is almost unknown
of high absorbance an excellent tain drugs
(Walker et al., 1981).
skite are not mineralogically
of
concen-
however.
as For
is one of the few habit
Palygorskite's
property makes it
food supplements,
The asbestiform
different
in
asbestos,
than that of kaolinite) dietary
all
Some are available
in other than asbestiform
in cosmetics,
prop-
and possess
in sufficient
applications,
et al., 1962).
(ten times greater
ingredient
in
number of other habit
of commercial
(also known as attapulgite)
(Marshall et al., 1942; Huggins
desirable
cannot be used commercially
They may have other industrial
example,
habit,
crystallize
all the properties
but are not available
fibers which
Today
in indus-
are known to both crystallize
and possess
in the asbestiform
for industrial
quantity,
utilized
When minerals
There are also a significant
which may crystallize
the properties
the industrially to be responsible
some or all of the industrially
Only a few minerals
asbestos.
and mechanical
term, asbestiform
mineralogical
crystallization
they develop
properties,
low thermal
(Zoltai, 1978).
term applied to fibrous minerals
a unique
commercial
also appear
This
carcinogenicity.
with this habit in large quantities
minerals
Ironically,
of asbestos
asbestos was the name of a mineral
it is a commercial
this habit,
of exploitable
high chemical
incombustibility.
property,
minerals.
and flexibility,
high adsorbency,
properties
undesirable
Initially,
combination
shape, high strength
conductivity,
physical
specifies
an unusual
industrial
and cer-
fibers of palygor-
from the fibers of commercial
asbestos. It is most unfortunate, latory agencies
have adopted
than the mineralogical known commercial
one.
asbestos
however,
that health scientists
the commercial Consequently,
minerals
definition all particles
are considered 237
and regu-
of asbestos
rather
of the five
to be asbestos,
pro-
vided that they have elongated or greater),
regardless
shapes
(with an aspect ratio of 3 to 1
of their asbestiform
this misconception,
asbestiform
and their potential
carcinogenic
crystallization.
fibers of other minerals properties
have not been investigated.
FIBROUS AND ASBESTIFORM These terms, fibrous
separable
with a fibrous
presence
properties
of asbestos
These are (I) hair-like cross sections
are exceptionally luster.
more durable
The development
strength higher
asbestiform
than that of single crystals
fibers usually
crystallize
aggregation. The dolumnar
The columnar
fibers.
adamantine
or silky
more flexible
crystallized
and
in other habits.
is gradational,
commercial
but they
asbestos.
The
of easily separable diameter
fibrils.
may occur in different
(3)
The
fibers and/or
Asbestiform
habits of crystal
habit is the most common.
growth habit
Most commercial
asbestos
crystallizes
in columnar
columnar
widths.
to the wall of the veins are referred
Fibers perpendicular
as cross fibers.
Inclined
The common commercial
tubular pattern,
in which
or scroll-like
asbestos
minerals
are chrysotile,
and cummingtonite-grunerite.
the layered
patterns.
this asbestiform
in veins of differing to
fibers are called slip fibers.
actinolite-tremolite,
is a serpentine
arrangement
aggregation.
Fibers are found in parallel,
riebeckite,
Their
and their faces
of the same minerals.
of smaller
qualities
the
fibers may be as much as 50 times
in bundles
fibers which are composed fibers of various
unusual
properties
in high-quality
of well-developed
organic
or irregular,
fibers are stronger,
of these physical
is more
this resem-
of its unique properties.
shape resembling
than the same mineral
are always well developed
Although
of the fact that the character-
circular,
smooth and may display
(2) The asbestiform
usually
contains
in the past, it implied
by virtue
elongated
actually
the term asbestiform
is a consequence
may be polygonal,
a mineral
habit if it gives the appear-
asbestos.
to visual observation
of asbestos
istic appearance
must resemble
synonymous:
the mineral
On the other hand,
the mineral
blance was limited
are'not
of fibers, whether
fibers or not.
restricted:
HABITS
and asbestiform,
is said to have crystallized ance of being composed
Due to
are neglected,
structure
Because
serpentine
Chrysotile
is curled up to form
of the unusual
is considered 238
anthophyllite,
structural
a distinct
mineral,
called chrysotile. boles.
The other commercial
The asbestiform
crocidolite.
variety
Historically,
of riebeckite
crocidolite
bole which has a valid varietal before
the parent mineral
the two minerals of crocidolite introduced
deposits
that "amosite"
is not a distinct
in South Africa.
form varieties
of actinolite-tremolite
that the name "amosite
(Fleischer,
1949).
In addition
to the well-known
discredited
commercial
known to crystallize
form habit
and possess
on occasion,
named nemalite.
He claimed
cause of its "asbestos-like asbestiform
brucite
the asbestos taining
sepiolite
mined
comparable
firmed to be primary
MacAdam
tubular
gorskite
Ten years later Tarnovskii and extremely
The chrysotile-like
structure asbestos
cluded that asbestiform of economic bestos
size could be found."
from Texas was described
by Dietrich
tourmaline
asbestos
of tubular halloysite in electron
micrographs
The good quality
of paly-
et al. (1962); they con"if deposits
Good quality potassiurn-winchite
239
has
was also found to have similar
would make good asbestos
recently
con-
et al., (1976) also found
observed
by Huggins
palygorskite
were
long asbestos
as tourmaline
structure
Imogolite
of
talc was later deter-
some occurrences
flexible
(Cradwick et al., 1972). was described
(1877) identified
on the occurrence
Some eight-inch
were identified
et al., 1978).
of
(1886) gave the name of agalite
most asbestos-like
long been known and has been repeatedly (e.g., Kohyama
to identify be-
thick veins in Utah as copper-con-
(1943) also reported
talc asbestos.
some fine (1 µm diameter) in pegrnatites.
Chester
after chrysotile,
fibers found in Switzerland
properties.
is difficult
Although
to be pseudomorphic
asbestos
in New Jersey which he
Many other occurrences
in Arizona.
talc.
et al.. (1966).
brucite
there
asbesti-
that nemalite
Kauffman
asbestos
minerals,
appearance."
he found in two-inch
to asbestiform
asbestos
to commer-
as a valid mineral
in the columnar
have since been found.
sepiolite.
in
of asbesti-
• • . should be restricted
(1821) found some asbestiform
was
occurring
and curnmingtonite-grunerite.
are many other minerals
Nuttal
structure
(1948) demonstrated
but is a mixture
cial use," and thus "amosite" was promptly name
of
The name amosite
(1949).
Rabbitt
mineral
amphi-
The identity
(Hall, 1918) for a mineral
major asbestos
name
it was known by that_name
until the crystal
by Whittaker
name
are all amphi-
has the varietal
was discovered.
was not firmly established
was determined
minerals
is the only asbestiform
name, because
riebeckite
as a new mineral
He proposed
asbestos
by Wylie and Huggins
as-
(1980).
A number of other minerals
are also found in asbestiform
Some of these have limited
asbestos
most commercial
Gruner
asbestos.
or fibrous minnesotaite not unknown
asbestos
properties
Reutelspacher of fibrous fibrous.
(Rutstein,
Fibers in different flexibilities. referred
Similarly,
to as "brittle
asbestos
and Zussman
tine layers
may only
This was illustrated
and display
fibers are frequently
type of serpentine
(1976), is composed
of segments
(Fig. Ib); it is called "polygonal
by Veblen
Some serpentine
structures
Such serpentine
A special
in 1796.
of chrysotile
(Fig. la).
and
is
The latter is
by Saussure
structure
process.
strengths
for example,
or "byssolite."
tubular or scroll-like
properties.
to be
and amesite
different
asbestos,
asbestos
in some samples.
to as picrolite.
by Cressey
asbestos"
or scroll-like
fibers have no obvious
referred
possess
(1979a) in electron micrographs
low-quality
micrographs
by fibers is a gradual
amphibole
for poor-quality
developed
electron
not considered
hydromagnesite,
properties
developed
good
"amosite").
stages of development
the tubular
be partially and Buseck
of asbestos
Poorly
the name introduced
(1968) show several which are usually
for discredited
reasonably
1979,; Guven et al., 1980).
calcite, nontronite,
These include
is rare, but
Certain micas were also
1978).
1979; Zoltai,
and van der Marel
The development
usually
1957; Frondel,
than
to asbestiform
Fibrous quartz
in fibers, and some of them display
crystals of minerals
(not to be mistaken
and are more brittle
(1946) makes references
and stilpnomelane.
(Braitsch,
found to crystallize
properties
habit.
fibers,
described
of planar serpen-
serpentine"
or "Povlen
chrysotile. " The reticulated
growth habit
In a reticulated are interlaced texture
to produce
of textiles.
component,
although
The layers of woven names,
growth habit, bundles
the interlaced
a layer of limited
In these sp~cimens occasionally asbestos
such as "matted asbestos
structure
are of high quality
asbestos
resembling
is usually
are strong and flexible,
chrysotile"
The fibers in the matted
thickness,
or "mountain is extended
the
in the lace.
and go by varietal
leather."
In some cases
in the third dimension.
cork."
chrysotile and provide 240
length
the only
some crystals may be "caught"
In such cases, it is called "mountain
example,
of fibers of varying
of the Coalinga commercial
deposit,
for
ore (Mumpton and
b
0·2 fJrr Figure 1. (a) Photograph taken by transmission electron microscope (TEM) of partially developed chrysotile fibers grading into planar serpentine. (After Veblen and Buseck, 1979a.) (b) Polygonal serpentine fibers. (After Cressey and Zussman, 1976.)
Figure 2. (a) Transmission electron micrograph of the replica Mumpton and Thompson, 1975.) (b) Scanning electron micrograph leather" from Templeton, Canada. (Photo by D. S. O'Hanley.)
241
of a chrysotile of palygorskite
matt. (After "mountain
Thompson,
1975).
Figure
2a illustrates
tern of fibers in the Coalinga matted bestos
mineral
in mountain
first identified
lea~her
by Heddle
the attractive chrysotile.
interlacing
The most common as-
is palygorskite,
as that which was
in 1879 (he called this mineral
pilolite
it was later found to be identical
with palygorskite).
Sepiolite
in mountain
rare but not unknown
(Caillere,
leather
are relatively
Actinolite-tremolite Frondel
is more common
(1980) most mountain
actinolite-tremolite. currently mountain
referred leather
The radiated
to as matted
Usually
and only a few are actually
or fibrous
the longer
are acicular,
habit is
it was previously
crystals
called
grow from what is ap-
joined at the center.
crystals. which
fibrous
Radiated
and of anthophyllite their asbestos
caused by the separation The massive-fibrous
strength
fibrils.
growth habit may be considered aggregation
fibers in straight
groups and the bundles between
nephrite
appears
and curved bundles.
Both the
The best example
jade, nephrite
of
(actinolite). but on a
texture of nephrite
and electron
242
However,
and there is
glassy and massive,
The fibrous
by many investigators,
This is because
pattern.
have random orientation
habit is the amphibole
samples
habit.
in radiated
the loose ends of fibers.
scale it is fibrous.
been observed
tensile
growth habit
they may also contain
In macroscopic
common.
are poorly developed.
of fibers along the shorter
class of the radiated
the massive-fibrous
fibers of
are relatively
fibers have low apparent
the fibers in this habit are frequently
some interlacing
The crystals
asbestiform
properties
In most cases the massive-fibrous to be a special
common aggregation
chain structures.
or asbestiforro.
developed
by crystals,
Most of the crystals
This is a relatively
have distinct
In most cases, however, Even the better
of a sphere.
from the center, and fill the space
cummingtonite-grunerite
microscopic
to
1936).
of a sphere is represented
start at a distance
habit of minerals
radiating
1936).
shear zones are
in the reticulated
a central point along the radial directions only a small segment
are shorter, between
chrysotile,
1908; Caillere,
fibers
1908), and according
found in marble
chrysotile
--
growth habit
In this habit acicular parently
leathers
Although
(Fersmann,
(Fersmann,
pat-
micrographs
has
have been
Figure 3. Photographs taken by scanning electron microscope (SEM) of (a) nephrite. (After Bradt et al., 1973.) (b) Meerschaum from Norway . (Photo by D. S. O'Hanley.) (c) Polarized light micrograph of massive-fibrous minnesotaite from the Mesabi Range, Minnesota. (Photo by T. Sabelin. )
published
(Bradt et al., 1973; Rowcliffe
and Fruhauf,
1977).
While the
fracture surface energies of silicates are on the order of 3,000-5,000 2 , Bradt et al. (1973) found that the fracture surface energy of high-quality nephrite is over 200,000 ergs/cm2. Figure 3a is a reproergs/cm
duction
of their scanning
electron
microscope
(SEM) photograph
(It should be noted that Bradt et al. found that the crystals
of nephrite. in jadeite
jade are not fibrous, and that its fracture surface energy is still over 2 100,000 ergs/cm • The possible reason for the toughness of the nonfibrous pyroxene apparent
jades will be discussed
differences
in the mechanical
243
later in this paper.)
properties
of different
The nephrites
may be attributed asbestos
properties
character
et al.,
habit
their jade-like
properties
fibrous
of meerschaum
(see Fig. 3b).
as "bowenite" crystals.
were
later identified
between
durete."
More recently,
in an electron
the fibers of chrysotile
and the bundles
of serpentine,
and bowenite
by Dana
known
some fibrous was recognized
as "nephrite," (1950).
but they
Caf.Ll.e re (1936)
and commented
(Braitsch,
(Fig. 3c) approaches and curved platy
microscopic
between
on the bowenite
study, Huggins
(1962)
serpentine.
the two is that in chrysotile
and in the massive
are randomly
texture
oriented.
1957; Frondel,
serpentine
they are
The fibrous microstructure 1962) is again similar
of nephrite.
The compact variety
the toughness
of jade and is composed
to
of minnesoof both
crystals.
fiber growth habit
In the habits diameter
lOX
varieties
with those in a massive
difference
the characteristic
Isolated
to be seen with a simple
oompacte qui xappel.l:e Le jade, sans en avoir La
of some chalcedony
taite
The be-
nephrite
the fibers are long and parallel,
fibrous
although
recognized
to these minerals
and named bowenite
ffe found that the major
shorter
less spectacular.
may also contain
study of the serpentines
a "texture
as having
asbestos
1980).
has long been
large enough
(1822), who referred
made an extensive
compared
(sepiolite)
serpentine,"
The similarity
by Bowen
asbestiform
of amphibole
et al.,
of
by the observation
is also found in other minerals,
Some glassy, massive
or "precious
The possible
characteristic
are, in general,
cause the fibers are usually loupe
and the quality
is also supported
1976a; Mallinson
The massive-fibrous
texture
components.
in nephrite
and other defects
(Hutchison
in the texture
of the fibrous
of the fibers
of chain-width fibers
to the differences
discussed
and usually
seminated
thus far, the fibers are always
occur in bundles.
Most of them, however,
are thicker.
be composed
fibers
of smaller
Fibers which as "capillary" speaking,
are larger
these larger
single
and possess
have comparable
fibers,
single
crystals may
but most are single
crystals
are usually
crystals. referred
crys tals, ins tead of "fibers." crystals
244
to
Strictly
are not asbestiforro.
small diameter
the properties
dis-
diameters.
Some of these thicker
or fibrils,
diameter
or "filamentary"
Most of the isolated of fibrils
Some individual
in rocks or grown in cavities,
small in
asbestiform
of commercial
fibers are composed asbestos.
Some
mineralogists
prefer
to describe
stead of asbestiform (Trendall
and Blockley,
of isolated product
1970).
is sold as asbestos
this distinction
except Dana
(Mumpton
asbestiform
and then the
1976).
Consequently,
of these crystals
growth habit.
crystal dimensions.
for not aggregating
elastic."
criterion.
to those fiber-sized
crystals
properties.
or filamentary
in bundles, described
Individual
in a meteorite
in-
ore
in some cases the concentration
and Thompson,
(1914), for example,
crystals
were identified
commercial
to justify mining,
can be found in isolated
of fiber, capillary,
capillary
However,
should be restricted
do not possess
properties,
fibers as "fibrous"
does not appear to be a valid mineralogical
Many minerals
asbestos.
these isolated
they do not constitute
fibers may be sufficient
The term "fibrous" which
because
Their physical
resemble
millerite
fine crystals
those of
as "brittle; of wollastonite
et al. (1979).
by Miyamoto
ranged between
They may be
The diameter
0.5 and 5.0 µm, and the authors
re-
ferred to them as "whiskers." Synthetic
asbestos
Most attempts phiboles
and whiskers to crystallize
synthetic
devoid of aluminlXffi and with
fluorine
(e.g., Shell et al., 1958; Nadgornyi
inorganic
compounds
have been synthesized,
synthetic
asbestos,
e.g., the potassium-lead
"hair-like"
terms "synthetic trary.
or simple
asbestos"
Most synthetic
sphalerite, peric1ase,
halite, quartz,
and "whiskers"
whiskers
sylvite, forsterite,
etc.).
interesting
to note that the whisker
(ll%) is synthetic
occurrences
forsterite
The basic physical asbestos
The natural-synthetic is recognized
silicate
is strictly
Fibers of many other
fibers of Shell "filamentary," between
semantic
equivalents
or the
and arbi-
(wurtzite,
corundum, brome11ite,
zincite,
Some are also known to have
(e.g., wurtzite possessing
and brucite). the highest
It is
strain rate
(Sears, 1962).
properties
fibers.
for hydroxyl
The difference
have mineral
fluorite,
natural
am-
but only a few were labeled
"whiskers."
asbestiform
of mineral
substituted
Most others are called "needle-like,"
crystals,
have involved
et al., 1965; Fedoseev et al., 1970).
to as synthetic asbestos.
These fibers were referred
et: al.. (1957).
asbestos
of whiskers
Some whiskers
correlation
between
by most investigators,
to those
may even grow .in bundles. whiskers
inasmuch 245
are identical
and asbestos
as they include
usually
asbestos
in the list of whiskers, Several
mineralogists
Frondel,
under the heading
have also accepted
1978) and a more extensive
by Walker
and Zoltai
character
single
into acicular
fibers and acicular
The fibers are extremely fragments
cleavage
Practically
all amphibole optical
asbestos
parallel
(riebeckite,
between
amphibole
the
in which
mineral
named
of two monoclinic
am-
of the common monoclinic
actinolite-tremolite,
property
(1928)
(It was later in 1948 that
is a mixture extinction
the ex-
crocidolite,
the asbestos
amphibole.
that "amosite"
This peculiar
Peacock
described
as "a monoclinic
angle is zero" and "amosite,"
demonstrated
discriminate
amphiboles,
to the fiber axis.
of riebeckite,
is a distinct
cleavage
in proper-
monoclinic
study of amphibole
asbestos
the acicular
differences
crossed Nicols
Rabbitt
amphibole
different.
Under
(1918), as an orthorhombic
grunerite)
while
to cleave
the individual
including
by Hall
phiboles.)
However,
are strikingly
asbestos,
of the fibers is parallel
the extinction
fragments.
properties.
tinction
variety
fibers
mineralogists.
orthorhombic
asbestiform
smaller
stress required
Such conspicuous
displays
in his classical
as-
is the conspicuous
fragments
strong and flexible,
intrigued
of amphibole
into increasingly
to the higher
cleavage
are weak and brittle.
ties obviously
is given
ASBESTOS
properties
Most evident
of bundles
This is in contrast
crystals
asbestos
(Taber, 1916;
of the comparison
OF AMPHIBOLE
of the physical
of easy separation
and fibrils.
account
STRUCTURE
bestos has long been recognized. property
that relationship
(1979).
THE UNIQUE The unique
of "cleaving whiskers."
and curnmingtonite-
of these fibers and can be applied
their asbestiform
and nonasbestiform
to
varieties
(Wylie, 1979). The apparent monoclinic whose
orthorhombic
amphiboles
chain directions
Supporting
observations
patterns.
Wylie
optics of -the asbestiform
imply that the fiber is composed are p.arallel but differently were obtained
varieties
of many crystals
rotated
from single-crystal
(1979) found that the reciprocal
of
lattice
about
fOOl].
diffraction points in the
[001] zone of thin actinolite
asbestos
Weissenberg
patterns.
(1979) found the same effect in precession
photographs
of thin (10 µm diameter)
Zoltai
fibers form a continuous
fibers of grunerite
246
line in
asbestos.
The «100» phibole
twinning
crystals.
twinning
However,
on the (100»
very thin.
is not unknown in monoclinic
In crocidqlite
and "amosite"
(Chisholm,
et al., 1976).
the orthorhombic satisfactory
of the cross sections ently,
studied
by Veblen
boundaries
observed
containing
different
Figure
chain-width
fully for the observed
to observe
of minerals.
resolution Iijima,
microscope
offered
It was known composed
however,
x-ray diffraction
triple
1980).
tetrahedral
fibrils
variations
microscope
it became structures
the high-
(e.g., Buseck and
One of the most exciting
from the layer structures
amphiboles
(jimthompsonite)
width,
were and
of the talcs and micas It was not known,
chains also exist. electron microscopy,
found two new minerals
details
and micas.
and amphiboles
this vo.lume).
tetrahedral
247
oriented can account
from the known average crystal
followed by high-resolution
chains
(99°)
properties.
electron
of pyroxenes,
see dhapter by Veblen,
et al. (1977), for example,
were
of differently
between
(like domain structures),
structures
that intermediate-width
Apparfibrils.
by Crawford
chains of single and double tetrahedral
that both were derivable (or vice versa:
fibers.
A more complex boundary,
that the I-beam units of the pyroxenes
of similar
observations
details of the crystal
unexpected
1974; Czank and Liebau,
was found in the crystal
microscope
was described
The presence
some deviations
for
A more
single-crystal
asbestos.
defects,
some of the minute
Although
asbestos.
and x-ray diffraction
structure were already accepted
1973, 1975;
4b shows one of these low-angle
With the advent of the high-resolution possible
faults
Franco et al. (1977) is repro-
types of boundaries
optical
(Chisholm,
types of grain boundaries
in anthophyllite
and of different
Stacking
asbestos
oriented
taken by Alario
(1980) and is shown in Figure 4c. fibrils
can be as thin as
faults may account
by electron
and flexible
The different
(1980).
crystals
of monoclinic
was offered
of brittle
photograph
duced in Figure 4a.
may be
fibers twin planes are
1979).
and stacking
the fibers contain differently
An excellent
asbestos
amphibole
properties
explanation
polysynthetic
faults on the (010) and (110) planes also
Twinning
optical
fibers,
am-
and the twin lamellae
1973; Whittaker,
to be common in fibrous
Hutchison
or acicular
the lamellae
in some tremolite
on the (100) plane and planar appear
asbestos
plane is frequent,
a few nanometers,while almost non-existent
in prismatic
which
Using Veblen
are composed
and of alternating
double
of
Figure 4. (a) Illustration of different crystallographic orientations of crocidolite f Lb er s in a bundle. (After Al.ar t o Franco et: al., , 1977.) (b) Low-angle boundary between anthophyllite fibers wit" triple and quintuple chain-width defects. (After Veblen, 1980.) (c) A complex boundary pattern between crocidolite fibers. (After Crawford, 1980.)
and triple
chains
observations boles
on the intimate
(Chisholm,
impetus
(chesteTite).
This name was introduced in 1970 to emphasize and amphibole
to [010]; these structural Thompson,
this volume.
using the mica modules chain bands
in 1911 and was revived by Thompson of the mica
as being
composed
relationships
A slightly of Thompson,
in the tetrahedral
of layer modules,
approach
in parallel
in the chapter by is followed here,
are the [010] single tetrahedral
(T) - octahedral 248
of the minerals
are described
different which
(biotite), pyroxene,
intermediates.
(1970), the structures
this group can be visualized
a strong
group name of biopyriboles.
and their possible
to Thompson
and
and amphi-
1979b, 1980) provided
of the mineral
by Johannsen
of these minerals
of micas, pyroxenes
and Buseck,
the similarities
structures
According
coexistence
1975; Veblen
for the recognition
The discovery
(M) - tetrahedral
(T)
units in layered silicates, cations
silicates.
or vacancies,
is one tetrahedral
chain, and their height
crystal
= nt;
T
layer.
structures
(t) is four times the height can be combined
displacement
n may be 0, 1/2, or 3/4.
where
can be recognized
The width of these modules
These modules
with a vertical
between
the pyroxene
occur, and when n alternatingly
subsequent
the sequence module
modules
the amphibole
Structural
The possible bole minerals descriptive
in amphibole construction
from basic scheme.
layer modules
conditions,
cause structural layer module
lization
may also result
module
defects
structural described
Oversaturation,
in Figure
of the biopyrithan a simple relationship pattern
the differences elevated
be-
temperature-
of these and other parameters incorporation
such "chain-width"
can
of erroneous
errors are comparable
structures.
in the development
Extremely
of similar
can grow almost
asbestos,
of different
rapid crystal-
errors.
instantaneously,
fibers may grow rapidly.
in amphibole
by Veblen
and
The layer
construction
conditions,
Whiskers and under
One of these reasons
of some or all of them may be responsible
continuity
The
in the same way that post-crystallization
tension
asbestos
or a combination
a close genetic
like the occasional
in close-packed
under one-directional some conditions
minor.
Genetically,
errors
structures
each layer module
and instability
faults,
combinations,
can.
structure.
is more important
range of crystallization
tween them may be relatively
are built. palygorskite,
are illustrated
of the crystal
Although
equals 0 and 1/2
asbestos
It also illustrates
among these minerals. has a definite
to stacking
produces
of the major biopyriboles
defects
reactions
structures
modules
0, 0, and 3/4 gives the sepiolite
constructions
pressure
are produced.
of n of 0 and 3/4 between
sequence
the
When n is equal to 1/2,
silicates
between
into com-
When n is equal to
zero, the major layered structures
of layered
layers and C interlayer
four types of layer modules
of an ideal polyhedral
modules,
the classification
the Di, Tri, DiC and TriC modules.
(Fig. 5):
plete
In line with
di- or tri-octahedral
which possess
for layer
as well as for the coexistence
biopyribole
minerals,
(1980) in the anthophyllite
occurrence
and
such as those at Pelham,
Massachusetts. The existence metric
crystals
of a certain
was suggested
type of planar
by Wadsley 249
defect in non-stoichio-
(1955).
These structural
faults
6.
o
D
a
D
J
i ~i i Di
DiG
Tri
TriG
C T M
T
Figure 5. Illustration of the four basic layer modules of the biopyriboles. The tetrahedra are completely rotated so that the anions are in close-packed sheets. Di = dioctahedral, Tri = trioctahedral, C = interlayer cation. The second octahedra in Tri and TriC modules are dotted. (Intermediate layer module, not shown, is ~~i, intermediate between Di and Tri; ~C indicates that one-half of the C sites are vacant.)
0
~
~
i;
I
0
~ Di-O pyrophyllite
Tri-O
0
~
0
0
0
0
0
0
0
o
i
0
.
0
0
0
0
~T=O 0
0
0
I
DiC-O TriC-O
talc
0
o
0
~ muscovite phlogopite
u ~ TriC-O-TriC-is
TriC-is pyroxene
(A site
amphibole
(TriisC-O-TriisC-is (A site
o
C cation
•
(OH) anion
@
H20 addi tional
TriisC-O-TriC-O-TriisC-is jimthompsonite
occupied)
not
amphibole)
occupied)
to
layer module
~Tri-O-~Tri-%
~Tri-O-Tri-O-~Tri-%
sepiolite
palygorskite Figure 6. Illustration of the layer module construction of the major mineral biopyriboles. Note that in pyroxene a half Tri and a half C cation constitute octahedra, and in amphibole two ~C cations make up the M-IV cation. 250
groups of the the M-II
are mistakes usually
in the ordering
referred
of crystallographic
to as Wadsley
defects.
of the b* diffractions
st~eaking
in amphibole
that as being due to the presence planes,
that is, Wadsley
defects
1976b) published
high-resolution
identify
defects
Wadsley
Subsequently, observed
electron
amphibole
actinolite-tremolite
It has also been
asbestos
quadruple-,
found in different
asbestiform
1976a,b;
et al., 1980).
Mallinson
300 times the single
Figure
1979b).
Most
(Mallinson
termination
in the biopyriboles
resemble
coherently
are accompanied
from
and Buseck,
chain defects (Veblen
"zippers."
were surveyed by Veblen
and
without
other
by displacive
displacive
resembling
fibers,
of these unusual
combined
in most non-fibrous hold the secret
termination.
coupled edge dislocations
crystals
to the unusual
of «110»
part in accounting
structural
with the apparent
amphibole
(1975) postulated
propagation
1978; Veblen
and quintuple
appear to terminate
pattern,
were
et al., 1980), is shovffiin Figure 10.
The observation
holm
quadruple
other terminations
of
(Hutchison et al.,
slabs of chain defects
zippers
defects;
patterns
chains, up to more than
Figure 9 shows a rather spectacu1ar
An interesting
et al.,
and sextuple-chains
fibers
Even wider
types of zipper terminations
(1980).
coordinated
antho-
as well as
double and triple chain structure
In c-axis orientation,
asbestos
or form different
quintuple-
amphibole
8 illustrates
of a disordered
The various
(crocidolite,
defects may not be limited
(Veblen et al.,, 1977; Buseck and Veblen,
in a matrix
faults.
fibers
chain width, were reported
and Buseck,
Buseck
layer defects have been
found that triple-chain
Furthermore,
1979b, 1980).
that clearly
and cumroingtonite-grunerite)
to layers, but rather may be isolated
Chester
microphotographs
layers in the (010) plane.
et al., 1980).
1978; Mallinson
grouping.
shear
et al. (1975,
(Hutchison et a~., 1976a; Jefferson
in the fibers of nephrite
the
fibers and interpreted
Hutchison
of triple-chain
in all the major
phyllite,
and are
(1973) observed
of faults in crystallographic (Fig. 7).
as triple-chain
the presence
shear planes
Chisholm
absence
strongly
properties
in amphibole
of the same features
implicates
of amphibole
that "the (010) Wadsley cleavage
details
defects
that they may
asbestos. inhibit
Chis-
the
cracks" and that they "may also playa
for the high strength ...
251
the most important
and
Figure 7. An early TEMphotograph illustrating Wadsley defects (N') in "amosite". (After Hutchison et: al , ~ 1974; as interpreted by Chisholm, 1975. )
.......... _-..c-
=.......... ·i. ... ....'= ~... ~
po--
.. -._
..
..
=1-"
~~ ~~~
""" """
~
~
::~ .. .... r-
~ 1.0 ~
~~....
~ It' ~
~
(3141 b 3 Figure 8. photograph
,
I""!-
~I-
II" ~
"'" ~
---~
~
..c
~
~ 31 3
I
33
1-= =~
-
-
.
II"
•
:~;;
=~~ ~:~::::
... ~~
Ii
~~
lit
~==..
3 3
Illustration of triple, quadruple, and quintuple chain of anthophyllite. (After Veblen and Buseck, 1979b.)
Figure 9. TEMphotographs and the interpretation "atpper s" in a c -axi.s orientation of anthophyllite.
252
== '..t:: ~t ~~ •• =~ =: '!:..... :~ ':,., :=~~ !i~ • C~ .: ... :lii .=
''1>"
1: ..
_La:
..,
~ ';:!ii ~: =: :. I: i-~
.'
~~
33 33
'
100 ...
Iloo
5 ==33:
width
defects
in a TEM
U&Ci
of a displacive fault termination of (After Veblen and Buseck, 1980.)
Figure 10. TEMphotograph and the interpretation of longitudinal termination of chain-width defects in a fiber of nephrite. (After Mallinson et: al , ~
1980. )
remarkable view.
properties
of asbestos."
He states that "the primary
dividual
However,
(from Chester,
for example)
"breakage
for the separation
observed
with TEM.
cleavage
along
Crawford
(010).
faults in crocidolites
he observed
of the asbestos
and require more force to complete plane.
Conversely,
fibers
faults"
is the was
for such along
(100)
propagated
in the
interference.
to connect
chain-width
properties.
the fracture
defects
The existence
to increase
the surface
of
energy
along the normal
it is also conceivable
253
along grain
such breakage
cleavages
and found that all cleavages
chain defects would be expected
cleavage
and stacking
(1980) found no indication
Instead,
of in-
that in some asbestos
of fibers and fibrils;
of (010) Wads ley defects without
with the development
for the formation
along the (010) chain-width
lamellae
At this point it is not possible
wider
(1980) took a different
of the crystallites
he also believes
errors and the (100) exsolution
presence
mechanism
fibers must be the separation
boundaries."
mechanism
Veblen
«110»
that there is a
significant tudinal
concentration
terminations
trations
could enhance
centrations,
however,
Whittaker planation Instead,
of stress around the misfit
of the chain-width the cleavage
of the properties
key
strength
of "cleaving
fibers with the observed
is increased
cracks in the surface along fibrils before
fibrils may be diverted they break
dislocation
of asbestos Zoltai
(Walker,
dissolution
1981).
irregularities dislocations
Whittaker
with Burgers vectors
It has been generally
In the following
section
by itself or through
responsible strength
for the strength
of the surface
mechanism
ic
structure,
the low density
appears
and
responsible
for
asbestos
structural
fibers as screw
that the exceptionally
and flexibility
growth
component.
of their low surface
structure
and has
was raised by Walker
("amosite")
from its internal
screw
The possible
high strength
defect density.
it will be shown that the surface
a fiber must be different structure
accepted
is a consequence
and
fibrils.
(1978).
a
Initial
between
in some amphibole
asbestos having
between
around a central
et al. (1981) have interpreted
in some grunerite
of the whiskers
observed
proposes
(1953) and by others,
as a possible
patterns
that the
the crystals.
to progress
fibers around screw dislocations
(1979), and was proposed
the unusual
by Sears
for quartz fibers by Frondel
defects.
to be found
The adhesion
across the internal
has been demonstrated
ex-
the longitudinal
Whittaker
than the bonds within
The spiral growth of many types of whiskers
been suggested
is perhaps
through
planes.
may exist in fibers.
is weaker
of the crystals.
about the possible
(1964)" who have demonstrated
whiskers"
situation
fibers and fibrils
the strength
to the problem
of cracks along the cleavage
that an analogous
edges and longi-
Such stress concenThe same stress con-
skepticism
of asbestos
that "The
in the work of Cook and Gordon
propagation
of fibers.
would also decrease
(1979) has expressed
he suggests
defects.
structure
of
that the surface
of surface
defects may be
of the fibers,
and that the
to affect the strength
of all
fibers.
THE SURFACE The bonding that inside
STRUCTURE
OF FIBERS
of atoms or ions on the surface must be different
the crystal.
The bonding
254
pattern
inside the crystal
from extends
in three dimensions.
However,
for the termination
there are only two dimensions
of the structure
on the surface,
ferent structural
scheme has to be developed.
crystallographers
speculated
tures.
of crystals which
on the possible
From their observation
structure
strength
were proposed.
of these concepts science
is heavily
During
dependent
but stronger
In order to balance
however,
the incomplete
porated
in the surface
a layer of exceptionally
ever, the surface LEED
structure.
structures
Several
features,
strength
structure
and
to crystal
the importance
structure
is
of the crystal.
bonds on the surface,
some bond dis-
atoms or ions may be incor-
Such modifications strong surface.
of bonding
Surface
may
structures yet.
How-
of other crystals have been studied by
Diffraction)
such as shorter
of the surface
block,
and modern material
fibers have not been investigated
(Low Energy Electron
structures
Mosaic,
that the surface
and additional
produce
or whisker
surface
decades,
struc-
strength
on their applications.
than the internal
shorter
of surface
of dislocations
the following
conceivable,
tances may become
of asbestos
of the crystals.
and the relevance
have been amply demonstrated,
It is equally not weaker,
patterns
study on defective
the weakness
concepts
In the early 1930's
of the lower-than-theoretical
arose a concentrated
could explain
lineage
available
and thus a dif-
and Auger electron
spectroscopy.
bond length, which may increase
structure,
have been observed.
the
The composition
of the surface
layer in small AIZ03 (corundum) crystals, for example, was found to contain higher cation-anion ratios. These ratios were found to be as high as Z:l, giving the formula of as AlZO Somorjai, stronger
1970).
Such an increase
cation-anion
structure
bonds.
was proposed
and others,
by Griffith
in reference
in the cation-anion
The possible
existence
(19Z1), Orowan
to the explanation
(French and
ratio suggests of strong surface
(1933), Weibull
of the strength
(1939),
of glass
fibers and whiskers. The increase mented
tutes an additional density
in the strength
by decreased
of surface
large number the density
surface
of the surface
defect density.
modification
of the surface
defects was observed
of authors. of surface
More recently,
defects,
structure.
in whiskers Walker
as illustrated
255
structure
can be aug-
This, of course,
consti-
The lower
by a relatively
(1981) has shown that by the density
of etch
Figure 11. Illustration of the dissolution of a grunerite asbestos fiber C'emcs t t e") in acids. This dissolution pattern indicates that the surface layer is more resistant to the acid than the fiber s internal structure. (After Walker, 1981.) I
pits, is lower in amphibole
asbestos
also found that the extended along cleavage fragments
dissolution
planes and produces
before
the dissolution
the complete
This is illustrated
of cleavage
subsequently
dissolution
of high quality
of the fiber and proceeds
than in cleavage
by the initial
development
relative weight surface
strength
of the surface
cleavage
By contrast, at the end
layer is dissolved.
of inverted developed
dissolution
cylindrical
of the two strengths
fiber is the composite structure
of the
of the fiber.
is proportional
The
to the ratio of the
That ratio increases
as the
of the fiber decreases.
The increasing observed similar
of an asbestos
and the internal
area and the volume of the fiber.
diameter
proceeds
11.
as shown in Figure
The overall strength
He
acicular
fibers is initiated the surface
cups at the end of the fiber and by partially structures,
fragments
smaller
of the mineral.
asbestos
inward before
fragments.
by Karmarsch observations
strength
of wires with decreasing
in 1859.
In the following
were reported.
glass fibers and on whiskers.
1969) involved natural
anthophyllite)
and synthetic
fibers.
face structure chrysotile
dominated
(chrysotile,
(~1g-fluorichterite
These experiments
and amphiboles
over a hundred
Most of these studies were done on
Only two investigations
1965; Aveston, asbestos
diameter was first
lZ5 years,
suggested
the strength (Fig. lZ).
256
(Nadgornyi
crocidolite,
et al.,
and
and Li-fluoramphibole)
that the role of the sur-
of both major types of asbestos,
o
o o o
40,000
"'-..--Q_
cgo
N C
u
B 0
? 30,000
Figure 12. The strength-diameter graph of some asbestos fibers. The circles are of Canadian chrysotile (Aveston, 1969). The squares represent a Russian chrvsc t fl e, the triangles a Russian anthophyllite, and the dots a South African crocidolite (Nadgornyi et al., 1965).
o o
o o
o
0
-;--0--0
0
o
000
o
Canadian 40
60
80
Diameter,
.":i 20,000
.
chryso t i l e 100
urn
~
..,
I~
'I'
~
I"
10,000-1-~'_
••
,
~~"1-'-, t"
S. African
·'loD::::.t:=.=
o
crocidolite
Russian anthophyll i te Russ i an chrysoti 1e
4
6
• .... 0 Diameter,
10
8
um
If we assume that the strong surface layer is only a couple of atoms deep and is uniform of the surface
throughout
and the internal
the fiber, the proportional structure
can be expressed
significance by a simple
equation:
(I) where Gf is the strength of the fiber, Gi is the internal strength of the fiber, K is a constant expressing the increased strength of the surface structure, length.
As is the surface
this equation
is not necessarily
but is a hypothetical face structures anywhere
area and V the volume of the fiber per unit
It should be noted that the meaning
of the internal
the strength
value of strength where
are in balance
strength
of the internal the internal
and the ultimate
in
structure,
and the sur-
fracture may be initiated
in the fiber.
In the majority
of the available
strength-diameter
measurements,
the
internal
strength of the fibers, G , is near the known "bulk" strength of i the glass or the single crystal strength of the corresponding inorganic compound
or mineral,
within
fibers may be referred
a range of expected
experimental
error.
to as type S (single crystal strength).
257
These
In some
34.321
30,,00
25,000
:E
20.JOO
rn c;
,_'" '"
.µ
15,000 13,218
Figure 13.
10,000
(2) .
Graphical
The dots
are
illustration
the
data
from
of equation
the
synthetic
Li-fluoramphibole asbestos cooled at the rate of 1.3°e per hour, and the solid line represents the linear regression of these pOints. The dashed line data of the
is the linear regression of similar same Li-fluoramphibole asbestos
cooled at the rate of 10°C per hour. (Data from Nadgornyi et al.~ 1965.) The values of 0i. of K" and of af at 1 11mdiameter are shown for each 0.0
0.4
0.2
0.8
0.6
1.0
set
of
synthetic
asbestos.
Reci proca 1 D, um
fibers the internal single crystal As expected asbestos
strength
strength
from their tubular
and graphite
fibers the internal crystal
is significantly
strength.
of the surface
greater
whiskers
strength
or scroll-like
structures,
are in this category.
chrysotile
In some other
is lower than the accepted
Yet, the fibers become
structure.
than the bulk or
to as type X (extra strong).
and may be referred
stronger
bulk or single
through
These fibers may be classified
the effect as type W
(weak) • Most fibers are either section.
circular,
square,
They have the same surface
D is either
the diameter
faces of square
of the circle, or is measured
or hexagonal
cross section
most fibers, .equation (1) can be simplified (Jf = (Ji(I The measurement fibers can be plotted Figure 13.
of the ultimate
+
fibers.
between
Accordingly,
that
parallel for
to:
4 Kj)
strength
is the ultimate
of the diameter
the linear regression
in cross
(Z) of different
diameter
into a graph format, such as the one shown in
The ordinate
the reciprocal
or hexagonal
area to volume ratio, provided
strength
of the fiber «(Jf)' and
(l/D) is the absissa.
of the data points 258
The Y intercept
of
gives the value of the internal
Table I.
The parameters of the mechanical synthetic asbestos fibers.
~
"1 kg/cm2
1=
~
.!5.
af
Projected ~
properties
Correlation coefficient
D=1µm
of natural
and
Number of points
Reference
28,700
+2. ,
+0.7
)106
0.68
30
Aveston
W
2,"50
+1.0
+0.1
127,000
0.88
11
Nadgorny1 ~.e_!.
(196
X
6,150
+0.6
22,100
0.77
28
Nadgorny1
(196
X
3,000
+1.5
21,000
0.31
31
Nadgcr-nyf ~~.
Mg-f!uor-r icbterite
S
2,950
+1.8
2" ,000
0.83
"6
Nadgornyi
~
.2.!..
(196
Li-fluoramphibole (cooling 1 oaC/hour) Li-fluoramphibole (cooling 1.3cC/hour)
S
1,650
+1.8
13,200
0.92
27
Nadgornyi
~
_g.
(196~
S
2,150
+3.9
35,000
0.92
23
Nadgornyi
~
g. (196!
Chrysotile (from Canada; Chrysotile (from Bazhenovskii) Crocidollte (from Africa) Anthophyllite (from Seysert)
X
-
(1969)
~~.
1
1
(196!
Synthetic:
-
(Oi)' and K can be calculated
strength
1
from the slope of linear regres-
sion line as:
D of
-
K
from South Africa
and synthetic amphibole.
asbestos,
The fiber parameters
of the regression
of amphiboles.
has more than double number
are insufficient
to justify
that this high internal generally
accepted
asbestos.
measurements
be in accord with the observed crocidolite
exception
provided
Although
by Nadgornyi
is the strongest
et al. to note
amphibole
also appears
of chain-width
and grunerite
which the
is in accord with the
of crocidolite
lower density
of
single-crystal
it is interesting
of crocidolite
strength
than in anthophyllite
strengths
is crocidolite,
of the others.
that crocidolite
internal
(Pearson Moments)
The internal
firm conclusions,
strength
opinion
The higher
good.
of
Russia,
from their
coefficients
the range of the expected
strength
strength
and an Li-fluor-
(Oi and K) as calculated
The only apparent
the internal
dependent
from Seysert,
Mg-fluor-richterite
The correlation
within
of strength-diameter
(3)
the diameter
lines are reasonably
the fibers are essentially
•
and anthophyllite
including
data are given in Table 1.
strength
(- 1) 0i
et al. (1965) measured
Nadgornyi crocidolite
4
asbestos
defects
to in
(Whittaker,
1979) • Equation whiskers
(I) cannot be satisfactorily
as the calculation
gives negative
259
used for a large internal
number
strengths.
of
Such is the
Ultimate strength
kg.!
cm2
20,900 20,000
/ / 15,000 ~=2.66
• 10, 000
5,000
.- - - . ... /_-/'l ••• _-
1,120
K=I.IO
/_
-
Figure 14. The strength-diameter graph of CU6SnS whiskers (Davies, 1964). The dashed line is the linear regression of these points, giving a negative value for internal strength. The curved, solid line is the exponential fit of equation (4) giving a realistic value for the internal strength of these whiskers.
_ 2,175
1.0
reciprocal
fiber diameter
urn
case of the Cu6Sn5 whiskers shown in Figure 14 (Davies, 1964). In these fibers the relative weight of the strength of the surface structure increases more rapidly with decreasing surface area to volume In the derivation
of the surface
than that allowed by the
ratio at any value of K. of equation
assumed to have practically weight
diameter
(1), the strong surface structure was
no depth.
With that assumption,
the relative
strength was related to the surface area of the
fiber, rather than to the volume of the surface layer.
There are several
other possibilities:
(a) It is conceivable
the surface structure
may extend deep into the fiber, through the de-
that the stronger bonds of
creased length of the more distant bonds.
(b) It is also possible
the small growth steps on the longitudinal
surfaces
fibers become shallower with decreasing concentration
as observed
fiber diameter,
around the steps diminishes.
and the stress
This theory was introduced
by Friedel in 1962 and Marsh in 1963 in order to explain strength effect.
(c) The increased
some fibers may also be explained
that
in some
weight of the surface
the diameterstrength in
by an indirect effect of axial cleavage.
Figure 15. Illustration of crack by the axial cleavage
260
the diversion of a "cleaving
of an initial whisker".
Cook and Gordon proposed
in 1964 that the propagation
may be diverted by the axial cleavage ers."
Figure
IS illustrates
of surface
in the so-called
how an initial
cracks
"cleaving whisk-
crack may be diverted
after
the first layer. The nature
and the geometric
causes for the increased However,
they are similar
effect on the fiber's
k.
This exponential
volume
expression
strength factor,
can be expressed
f
positive,
single-crystal
+
J.
the calculated
served a relatively
strength
factor,
area to
i
(4)
strength
that is comparable (Fig. 14).
of the Cu6Sn5 whiskers to the expected
Davies
(1964) ob-
of surface
steps in the Cu6Sn5 fibers, of the effect of these steps.
and the value of k may be an expression The increasing
to the surface
Ki) l+k D D
of this sulfide
high density
or combined
(Z):
internal
with a magnitude
strength
are different.
by an exponential
still proportional
= (J.(l
Ci
With this equation
structure
in the sense that their individual
ratio, can be added to equation
becomes
of these three possible
effect of the surface
of the chrysotile
fibers with decreasing
diameter
has long been known
(Cosette and Delvaux,
1979).
diameter
data of the Russian
chrysotile
(Nadgornyi
et al., 1965) and the
similar
data of the Canadian
chrysotile
tically
low values
(Aves ton , 1969) gave unrealis(e.g., 610 kg/cmZ for the Rus-
sian chrysotile)
for internal
when analyzed
strength
with equation
tion (4) was used more realistic
of the fibers.
The two sets of chrysotile
differences
in their mechanical
strength
of the Canadian
that of the Russian. chrysotile
appears
the chrysotile
chrysotile
The higher
is expected
of relatively
poor quality.
points of the Canadian of the Russian
chrysotile.
The internal
to be 10 times higher
strength
the strength
On the other hand,
structure
of
of the crystal.
of Nadgornyi the scatter
(Fig. lZ) is much broader
This may be due to differences
261
than
of the Canadian
as the rolled-up
that the chrysotile
chrysotile
In
fibers appear to have sig-
appears
to increase
when equa-
(Table I).
of the axial cleavage
properties.
internal
to be more realistic,
It is, of course, possible
However,
values were obtained
k may be a consequence
these fibers the constant
nificant
(1).
The strength-
et al. was of the data than that in the
Table 2.
The parameters of the mechanical properties which have corresponding minerals.
Projected at ~
Material LiF
4,250 120
KCl NaGl
90
NaCl
325
+0.4
+0.2
+0.7
+0.6
19,000
Or
Correlation coefficient
of selected
whiskers
Number of points
Reference
0.60
32
Fridman
and
2,250
0.71
22
Marsh
(1963)
200
0.23
11
Ewald and Polanyi
+1.7
3,500
0.75
55
Gyulai
NaCl
450
+0.5
1,400
0.66
18
Marsh
250
+0.9
+0.7
7,600
0.84
42
Gyulal~.!.!..
170
+1.5
+0.7
60,000
0.84
27
Gyulal
100
+2.9
+1.0
949,000
0.74
46
Gyulai ~
400
+6.1
+1.7 10,400
0.73
27
Evans
MgO
'1203 A1203
fiber
[100l
axis
X
A.l203 A1203
at
A1203
5,800
+0.6
5,000
+7.1
5,600
...4.1
+1.2
(1963) (1961)
~!l.
(1961)
ll'
llg.
147,000
0.79
11
Reinkober
)106
0.76
36
Campbell
(1931) (1970)
13,000
+2.1
123,000
0.70
46
Bayer and Cooper
+2.1
178,000
0.61
27
Mehan ~
2',000
+1.5
144,000
0.46
35
Mehan and Feingold
266,000
0.78
15
Brenner
(1962)
21..
at
1. 110°C
18,700
..2.5
205,000
0.66
28
Drenner
(1962)
1 ,550oC
14,500
+0.7
57,000
0.66
12
Brenner
(1962)
H203
at
2,030oC
",500
+0.5
36,000
0.20
10
Brenner
30,650
+2.5
341,000
0.62
32
Sutton
fiber
axis
X
(1967)
(1965)
at
[001]
(1965)
(1964)
A1203
A1203
(1961)
Wolff and Cockren
A1203
A1203
(1925)
19,000
25QC
(1963)
(1954)
NaCl (ceramic substrate) NaCl (foil substrate) NaCl (from alcohol actutdon)
ZnO
Shpunt
(1965)
(1962) (1970)
35,000
+0.5
108,000
0.38
34
Bayer and Cooper
A1203
36,000
+0.2
TOO,000
0.39
40
Mehan and Feingold
(1966)
A1203
38,000
+0.3
82,000
0.34
92
Mehan and Feingold
"967)
A1203
39.500
+0.6
139,000
0.60
33
Soltis
A1203
45,500
+0.5
130,000
0.39
26
Herzog (Mehan and Herzog,
A1203
49,500
...1.3
299,000
0.20
A1203
(1967)
(1967)
Cunningham
(1960)
58,000
+0.5
150,000
0.63
33
Kelsey
and Krock
(1967)
A1203
[001]
fiber
axis
X
73,000
+0.3
166,000
0.66
29
Bokshte1n
~!.!..
(1968)
A1203
(101)
fiber
axas
X
79,000
+0.2
146,000
0.49
62
Bokshtein
~
A1203 [100] or [110] fiber axis
90,000
+0.2
16,000
"'3.7
13,850
+0.9
7,150
...2.6
+1.2
C Graf1l
HT (1 ,50QoC)
C Grafi!
A
24,000
HT
23,000
+0.4
4,250
+2.4
1,800
+4.6
+1.3
+0.2
...0.1
C
GrafH
C Thornel C PAN -same
50
precursor at;
1 ,OOO-l,20QaC
S
25.400
+0.9
164,000
0.47
38
Bokshtein
)106
0.89
40
Regeat er
g.
ll!l. II _g.
ll!.!..
64,000
0.31
11
Perry
)106
0.80
98
Lamotte and Perry
24,000
0.31
96
Nicoll
0.08
92
Nicoll
0.40
36
Jones
+0.8
61,000
262
(1968) (1967)
(1971)
and Ferry and
(1968)
Pe r-r'y
(1970) (1973) (1913)
and Duncan
(1971) (1971)
0.4 ~
36
Jones and Duncan
0.04
82
Jones
(1971)
1970)
experimental control
techniques.
For example,
on the length of the fibers.
this puzzling
question
Unfortunately, diameter
category
of whiskers
Zoltai,
studies
are needed before
available
fibers is limited
are more numerous,
equivalents.
in Table 2.
of the surface
on the strength-
to two publications.
and many of the whiskers
The strength-diameter
is listed
ment and discussion
Further
of information
of asbestos
on whiskers
have mineralogical
did not employ a rigid
can be resolved.
the quantity
relationships
The publications
Aveston
data of the latter
(For a more detailed
effect on the strength
develop-
of fibers see
1981.)
Fiber length and strength The decreasing stant diameter, Reinkober
strength
was also observed
(1931).
in asbestos
of fibers with increasing by many investigators.
Figure 16 illustrates
fibers
to those obtained
(Zukowski
relationship
at con-
The first was
the same relationship
and Gaze, 1959).
for the diameter
the strength-length
length,
dependence
observed
These patterns
are similar
of the strength.
However,
is not directly
related
to the diameter
of the fiber. Two somewhat non.
related
One stipulates
fibrils,
and that premature
along these shorter are occasional fibers, defect
and that they cause a rupture below
Moreton
the observed
the expected
estimated
(1969),
(Tippett,
for example,
and calculated
263
defects
in the
stress.
These
as the length of
defect
concentrations,
of increasingly
1925; Pierce,
strength
longer
1926;
found an excellent
length-dependent
in some carbon whiskers.
that there
act like "weak links" in
fibrils,
their effect on the strength
can be statistically 1939).
of shorter
the fiber apart
postulates
to be more frequent
Both of these features
If the distribution
or both, are uniform,
between
will occur by pulling
of strength-reducing
are expected
for this phenome-
more short
The other explanation
high concentrations
concentrations
the chain.
fibers
have been offered
fibers contain
fracture
fibrils.
the fiber increases.
Weibull,
explanations
that longer
match
pattern
.OOI·~
800
0"'"
"'0
o 'a
...'" o
'" '"'"
QJ .D
"0
L: o
:.
...
>.
'"o u ...J
'-
QJ .D
u
E"'''
"' ...
.s:::. c·,...
... '-u"''' => o z
""" -'" QJ ....
'-
'" '"
E ... _ c( c· .... re en '- ~V') QJ N QJ 0'". ...0 .s: a: It:' 0._ rc Vl 0'. ... ,-,0::::1.., • ::::I '-~-=> ::> "" aJ ::> o V'>
-" rc.s:::.·,...
'" ttI::::IrcCtOrcQJ c: L· .... rc .,.....c.. "'0 C. rc.s:::. ~c rc
L
ra.c'µNCll
uE~"'.s:::.
·...._O~.µ
....
'-NVlV)
0
'" ...'"'-
c:>, QJ :J:..::.t. L... ..... c, 0 I'CI::J
c:
c,
""
QJ
'"
"'=
'0 -e
QJ""
u C
""
....
""
...
,~
';UU-"'":l:":::1-1-
""
10J
'"u
'L:
'-"c:
• >
QJ~
QJ
'"u ....
u
u
'",,"QJ
'"
~'"'- '"c:
'"
c,
o
~
M
il
u o 'u
QJ .D
'"
I-
~ ~
N C
er c o
c '"
N
C
g
co o
... o
~ c
...c:
C
C
~ _ ccc
~
_ ~ ecce
C 0 C eN N
N
o
~ ~ c
N
C
co c>
~
c;
C
C
z c
~ c
o
~
c c
c c
ccc
:~
IIIQ.lC_ Cl.>LOCIOII
'\:).1::
-
:; ~
"'_
QI
C:'"
....+'+-''"
QlC
.-
0
>,ct:
'" L OIl! Q.I_ ..... __",
'"
--~
;::!
C '"
G.I ..... .L:l
QJ
....
U 0 L U
C
L G.I +-,
.I:: .... __
> .....
+' C ftl
c:
:1:5
tC~~
~~i~~
~=~
~~~~ :~E
~L
LE
- .... .... Vl _
II >.U ~O
:::l
g_
-,;;:111
""'11'10.1::
C ..C"
o
E C O-
....
C
-_ o a;:J: c: 0
C~
~~ ~
~~~ ~~
0_ -0
O~
}'~~) e
iE~
g
•
,~~
0, o. -e
c
.
. " U~
~C~
L
~~ ~
~
""'u
0
~;::~o::
K
~~ . >~W LU_
Ill ....
.
~O~ D
Q)
KD
OWe
U
> o
OUN ~C~
~
o
>00_
O~ U_
0
O~ E' "0 ~O
~ ~ ~ ~
1::U"l
0.._
igins of Soapstone. asbestos.
In
- Mineralogy,
Revieue D.R.
323
Bull.
Commission
in Miner>alogy, Vol. Veblen,
ed.
[this
9A, volume).
Geologique
Finlande,
Amphiboles
and
Chapter SUBSOLIDUS
REACTIONS
7
and MICROSTRUCTURES Subrata
in AMPHIBOLES
Ghose
INTRODUCTION In this chapter we describe
the subsolidus
phenomena
in amphiboles,
which
include four different topics: (1) the thermodynamics and kinetics 2 of Mg_Fe + order-disorder in ferromagnesian and sodic amphiboles, (2)
miscibility
gaps and exsolution,
amphiboles,
and (4) thermal decomposition
phenomena dering
can be regarded
process.
solidus
lower temperatures,
rise to microscopic
is relatively
hence,
exsolution
reaction
textures
at these lower temperatures
trolled partial
water
problems,
significant
plication
of single-crystal
microscopy, mination
as well
of solvus
considerable
progress
crystal-chemical
pressures
a comprehensible
guiding
general
next decade most of the details will be clarified ogists working
through
take place at
are slower,
(~700°C or below) is difficult.
giving
Secondly, under con-
In spite of these
diffraction
techniques.
the ap-
and electron
Experimental
deter-
has been made in two cases; however,
the subsolidus chemical
picture
Nonetheless, phenomena
complexity
is emerging.
the
are fairly
of the amphi-
Hopefully,
of the sub solidus phenomena
a concerted
reasons.
effort of petrologists
in the
in amphiboles and mineral-
both in the field and in the laboratory.
THERMODYNAMICS
AND KINETICS
REACTION Mg-Fe
kinetics
to be done in this field.
clear, and in spite of the tremendous boles,
reactions
X-ray and electron
gaps in amphiboles
principles
for several
are much lower in temper-
has been made since 1960 through
as spectroscopic
work. remains
of the sub-
which may go unnoticed.
experimentation
and oxygen
of the cation or-
meager
the subsolidus
where
The first two
our knowledge
limits of many amphiboles
ature than the pyroxenes; relatively
expressions
with pyroxenes,
in amphiboles
the stability
in ferromagnesian
of amphiboles.
as two different
In contrast
phenomena
First,
(3) phase transitions
OF THE Fe2+_Mg2+
IN FERROMAGNESIAN
ORDER-DISORDER
AMPHIBOLES
in curnmingtonite and actinolite Anthophyllite
binary
and cummingtonite-grunerite
solid solution
belong
to an essentially
series, Mg7SiS022(OH)2-Fe7SiS022(OH)2' 325
with minor
amounts
of Al in anthophyllite
the difference different
and Ca,Mn in cummingtonite.
In spite of
in symmetry, the natures of the four crystallographically
octahedral
sites in both mineral
series are closely
comparable:
the Ml and M3 sites are nearly regular with 4(0) and 2(OH) as ligands, M2 is quite regular with 6(0) as ligands, torted
from the octahedral
ordinated
and by two more oxygens anthophyllite, oxygen
symmetry.
by four near-oxygen
of 2.757A
the M4 site is effectively distance
site plays a very special
five-coordinated,
of 2.08l±D.057A,
role in all amphibole
since it holds adjacent
Because
of the intrinsic
environments
the M4 site is co-
(Finger, 1969).
and two further ones at 2.865 and 2.867A
symmetry,
T-O-T slabs
differences
In
with
four
a fifth oxygen at
(Finger, 1970). structures
("I-beams")
in the chemical
The M4
regardless
of
together. and structural
among the different
amphiboles, equally
In grunerite,
dis-
atoms, two at 2.l35A and two at 1.988A,
at a distance
atoms at an average
2.387A,
and M4 is very highly
octahedral cation sites in ferromagnesian that Fe2+ and Mg2+ would be distributed un-
it was expected
among these sites
this yolume).
(see discussions
From single-crystal
by Hawthorne
X-ray refinements
in Chapter
1 of
of a grunerite
(Ghose and Hellner, 1959) and a cummingtonite (Ghose, 1961), it was found 2 that Fe + has a strong preference for the M4 site, Mg2+ for the M2 site, 2 2 and that Fe + and Mg + are nearly equally distributed in Ml and M3. Subsequent
X-ray refinements
and Finger
of cummingtonite
(1969) confirmed
sults, Ghose
this trend.
(1962, 1965) predicted
and grunerite
(1966)
Based on the cummingtonite
that anthophyllite
confirmed
by Fischer
ordering
trend, subsequently
by
infrared
troscopy
(Bancroft et al., 1966) and crystal
re-
would show a similar
and Mossbauer
structure
analysis
spec(Finger,
1970). Mueller actinolite
(1960) considered
and cummingtonite
Bloom Lake, Quebec, tribution
coefficient
Canada. between
the minerals
closely attained
tion between
coexisting
the Fe2+_Mg2+
distribution
from a metamorphosed
iron formation
From the smooth variation coexisting
mineral
The ion-exchange
and cummingtonite
~ ca~Fe~Si8022(OH)2
+ ~ Mg~Mg;Si8022(OH)2
i
+ ~ Fe~Fe~Si8022(OH)2
Ca~Mg~Si8022(OH)2
326
near
of the Fe-Mg dis-
pairs, he concluded
local equilibrium.
actinolite
in coexisting
that
reac-
is the following: ~ (a)
where
superscripts
tively.
V and W denote sublattices
The equilibrium
relation
M4 and (Ml,M2,M3),
for reaction
respec-
(a) is given by Mueller
(1962) :
K
~g (1 - ~g ) act cum ~g (1 _ ~g exp 0.40 (1 - 2~g ) cum act) cum
a
where
~g and ~g are the mole fractions Mg!(Mg+Fe) in actinolite and act cum cummingtonite, respectively. The value of the equilibrium constant Ka
was found to be 1.80. was explained tinolite
The observed
by Mueller
behaves
inter crystalline
(1961) on the basis of the assumption
as an ideal solution,
a regular solution
cation distribution
(Guggenheim,
whereas
1952).
cummingtonite
The deviation
that ac-
behaves
as
of cummingtonite
from ideal behavior was considered to be due to the strong site preference 2 of Fe + for the M4 site in cummingtonite, whereas this site is occupied bY'Ca
in actinolite.
Mueller
(1962) reasoned
that since the configura-
tions of the Ml, M2 and M3 sites are not very different lite or cummingtonite, Fe-Mg distribution
to a first approximation,
in cummingtonite
M4 site ("V sublattice") gether
("W sublattice")
spectroscopy
al.,
the intracrystalline
can be considered
to be between
on the one hand, and Ml,M2,M3 on the other.
of cummingtonite
has
the
sites taken to-
Indeed, subsequent
(Whitfield
1967; Hafner and Ghose, 1971)
in either actino-
Mossbauer
1967; Bancroft et failed to distinguish the Fe2+ and Freeman,
occupancies
of the Ml, M2 and M3 sites. Following Dienes (1955), Mueller 2 (1962) proposed a treatment of the Fe +_Mg2+ order-disorder in cumming-
tonite as an ion exchange
reaction between
we will denote as M4 and Ml,2,3, Fe
2+
Assuming
(M4) + Mg
2+
(Ml,2,3)
~
ideal solution behavior
rium constant ~
the V and W sublattices,
Mg
2+
(M4) + Fe
2+
(Ml,2,3)
.
(b)
at each set of sites, the equilib-
(b) can be written
for reaction
which
respectively:
as
xFe (1 _ XFe) -'Ml,2,3 M4 x!e (1
-'M4 where ~~
,2 ,3
and ~:
_
xF~ -'M]. ,
2 ,3
)
are the mole fractions
and (114) sites, respectively,
as determined
fraction
spectroscopy.
studies or Mossbauer
327
Fe!(Fe+Mg)
in the (Ml,M2,M3)
by single-crystal However,
X-ray dif-
to explain
the
observed
intercrystalline
a partially
regular
partitioning
solution
data, Mueller
(1962) postulated
model for cummingtonite,
where the mixing
of Fe and Mg in the W sublattice of mixing
is associated
is ideal, and all the excess free energy
with the V sublattice
(M4).
Matsui
and Banno
(1965), on the other hand, used the ideal site model to explain partitioning
between
coexisting
most general
case, where
actinolite
from ideal solution
can be written
as 'Ml63
For the
the mixing of Fe and Mg at the M4 and the Ml,2,3
sites deviates
xFe
and cummingtonite.
the Fe-Mg
behavior,
the equilibrium
constant
~
(1 _ XFe) -'M4
XFe(l _ xF~ ) -'M4 -'Ml , 2 , 3 where
the f values
Ml,2,3
are the partial
activity
coefficients
for Fe or Mg in
or M4.
We now have to define the partial (1964) has considered of which behaves volving
two coexisting
as a regular
solution.
two ions A and B between
K can be written
activity
phases
coefficients.
in equilibrium,
For an exchange
the two phases,
Mueller
S,
a and reaction
the equilibrium
each
in-
constant
as
(l-X~)X~ exp [(1-2X~)~!RT) K
(l-X~)X~ exp where
[(1-2X!)W~!RT)
,
X~ is the ionic mole fraction A!(A+B)
sponding
mole fraction
in phase
ciated with phases a and If we consider in ion-exchange equation
S, "v"
equilibrium
"w"
within
sublattices
to be coexisting
the cummingtonite
asso-
subphases
phase, the above
form:
[(1_2XFe )WMl,2,3!RT) -'Mlo 2, 3
are mole fractions
and the M~ ~ite respectively;
WMl,2,3
now in the form
328
Fe!(Fe+Mg)
at the Ml,2,3'
and WM4 are ion exchange
associa ted with these si tes, respectively. can be defined
energies
respectively. and
Fe Fe XMl ,2 , 3(1 - XM4) exp Fe Fe (1 - XMi,2,3)XM4 exp
2 3 and~:
in phase a and X~ the corre-
Wa and We are exchange
can be recast in the following
K
where ~~
the
S.
The partial
sites
energies
acti vi ty coefficients
1.0.
-r - oT~
r-
---f--
0.9
aB '0.7 ;:;:- 0.6
~
;t
Lt
0.5
0
v~
0
/
I
0..3
a
I
~~~
0.4
a.
r= - [2JLt-
[7!.f"
I
_H
-v~_
t,L -A1/ / I I
0.2
Pot7
~+'
_
V
Figure 1. Fe2+_Mg2+ distribution in the M4 site and the set of sites MI., M2, M3 in cummingtonites. Squares are samples from Butler, crosses samples of Klein, open circles samples of Mueller, and solid circle sample of Kisch. The solid curve is the least· squares fit to the data based on a regular solution too del ; the daShed line is an ideal solution eode'l. From Hafner and Ghose (1971).
,
1/
•~- •
1/
-
I
I
0.1 0.2 0.3 0.4 0.5 0.6 0.7 o.B 0.9 10 _ Fe2+(Ml,M2,M3)
WMl,2,3
Fe
In
RT
Fe )2. (1 - XMl,2,3
solution
model of Hildebrand
fMl,2,3
This is the regular (1952), which
implies
that the entropy
of an ideal solution with
and that the partial
the square of the concentration,
The two heat constants
WMI,2,3/RT
and (M4) sites, respectively. as a measure
at each site is that
molar heat of mixing varies
but is independent
and WM4/RT
of temperature.
are associated
The magnitudes
of the deviation
(1929) and Guggenheim
of mixing
with
of these constants
of Fe-Mg mixing
(Ml,2,3) serve
at each set of sites from
ideal behavior. Although
Bancroft
number
of cummingtonites
served
distributions
et al. (1967) determined by infrared
Fe-Mg distributions
and Mossbauer
showed a large scatter,
spectroscopy,
and a test of these thermo-
dynamic models was not possible.
Subsequently,
determined
in 26 cummingtonite-grunerite
the Fe-Mg distribution
ranging
in composition
derived
from the metamorphosed
Klein,
1966; Butler,
brated
amphibolite
served
Fe-Mg distribution
allow testing
solution
1969).
rocks,
data would
of the postulated
specimens
(Mueller,
1960;
came from well-equili-
it was expected
that the ob-
show a smooth trend, which would
thermodynamic
data, which
(1971)
all except one being
of Quebec
Since these specimens
facies granulite
the Fe-Mg distribution
Hafner and Ghose
from 0.96 to 0.18 Fe/(Fe+Mg), iron formations
in a
the ob-
models.
can be approximated
Figure 1 shows by a regular
modeL
If we consider the Mueller (1960) samples only, the equilibrium . M4 Ml 2 3 constant lS 0.19, and ~- /RT and W ' , /RT have values of 1.58 and 0.54, respectively
(Hafner and Ghose, 1971).
329
In rocks studied by Mueller
16
(1960), the oxygen
isotope
magnetite
a "quench-in"
indicate
ratios 0
18
/0
temperature
(Sharma et al., 1965) .• This represents of formation within
of these rocks.
slow cooling
crystalline
Fe-Mg exchange
iron formation exchange,
(see below),
can be calculated
quartz and
for ion exchange
of 600.±20°C
that the Fe-Mg ion exchange
to lower temperatures,
of a regionally
assume 425°C to be the effective
coexisting
a lower limit for the temperature
It is expected
the crystals will continue
of reasonably
between
as a function
metamorphosed
"quench-in"
rock.
temperature
for cummingtonites
If we
for the intra-
from the metamorphosed
then ~Go, the Gibbs free energy of the ion from the relationship
~Go
=
-RT In K as 2.32
Kcal/mole. The rocks from Klein's at a higher
temperature
they contain
orthopyroxene
with cummingtonite, (1966) samples with
(1966) and Butler's
as a thermodynamically
actinolite
the distribution
therms in natural ing in composition
coefficient
K
=
If we consider
the Mg-Fe distribution
at 600 and 700°C.
from 38 to 84 mole percent
sites was determined
mixing of Mg and Fe is regular constants, K, JM4 and ~,2,3 respectively Kcal/mole.
(Fig. 2).
model
0.092.
Cummingtonites,
Fe7Si8022(OH)2'
with 3 wt % H20 in silver capsules and were equilibrated total pressure (90% Ar, 10% H2). The Mg-Fe distribution (Ml,M2,M3)
Klein's
using an ideal solution
(197lb) have determined
cummingtonites
(1960) area, since
stable phase coexisting
and clinopyroxene.
only, a good fit is obtained
Ghose and Weidner
(1969) areas crystallized
than the rocks from Mueller's
by Mossbauer
at each set of sites.
rang-
were sealed
under 2 kbar at M4 and
spectroscopy.
at this temperature
iso-
At 600°C the
The equilibrium
are 0.26, 1.09 and 1.23,
The Gibbs free energy change at 600°C is 2.35
On the other hand, if we assume an ideal distribution
to be valid at each set of sites, the equilibrium Gibbs free energy change, ~Go, obtained
constant,
model
K, and the
from Ghose and Weidner's
data
(Fig. 3) are:
The enthalpy
T(OC)
K
600
0.106
3.9
700
0.153
3.6
~GO(Kcal/mole)
change, ~H, is estimated
small contribution
to be ~3.6 Kcal/mole,
of the configurational
330
entropy
indicating
to free energy.
a
In view
~o_o_c5>0.8
o
T= 600°C = 0.26 WM4 1.09 WIl1,2,1I= 1.23
K
=
Figure 2. Fe2+-Mg2+ distribution isotherm in heat-treated cummingtonites at 600"C. The solid curve is based on the regular solution IOOdel. From Ghase and Weidner (1971b) •
XFeMl,2,3
V., :!ELL
X
Figure 3. Fe2+_Mg2+ distribution isotherms in cummingtonites at 600 and 700 e. The solid curves are fits to the ideal solution model at each set of sites. From Chose and Weidner (1971b). 0
G
0.2
0.0 L---L---:-'-:--L-:-Il__...1---:-l_-'----L_L-~ 0.0 0.2 0.4 0.6 0.8 XM1,2,3 Fe
InK -25
-20
-15
o DH7-482
-10
o 10141
Figure 4. Plot of Zn K versus liT for haa t ed cummingtonite samples. Slopes of the curves yield _6.Ho/R. From Ghose and Weidner (1972).
" 118125
-05'A~~'6~L_~8~~fO~L_~1'2~~f~4_L-+1'6~~I'~8_L~2D~~ 10'/T('K)
331
1.0
of these results, librated
it would
appear
that Klein's
in terms of intracrystalline
ture slightly
(1966) samples were equi-
Mg-Fe distribution
at a tempera-
less than 600°C.
To be able to use the Fe-Hg order-disorder geothermometer,
Ghose and Weidner
rich cummingtonites in Figure 4.
at various
(1972) heat treated
temperatures.
From extrapolation,
atures of the cummingtonites Table
1.
Estimated
in cummingtonite
three magnesium-
These results
the "quench-in"
as a
are plotted
equilibration
temper-
were as follows:
crystallization
and/or
equilibration
temperatures
of cummingtonites Rock type [sample no.]
Fe! (Fe+Mg)
Metatoorphosed iron-formation
--
Chlorite-amphibolite
Baltimore,
schist,
Chlorite-amphibolite,
(amphibolite
sample
The observed
Tc below which
low temperatures
to reflect Although
c
ruled out, in view of the kinetic subsequently
above interpretation
reported
and Virgo
order-disorder
between
with the chemical using Mossbauer experiments
temperatures,
cannot be completely
data on Mg-Fe order-disorder
in antho-
(1974, 1975), the
rate of rocks
(1974, 1975) have studied M4 and Ml,2,3
composition
spectroscopy
At temperatures
the kinetics
sites in an anthophyllite
of Mg2+_Fe2+ from Montana
NaO.05CaO.09Mg5.79Fel.17(Si7.8lAlO.18)022(OH)2' at 77°K.
in the temperature
is attained within
that
for the other two
by Seifert and Virgo
and the cooling
seal bombs and with controlled buffer).
1960), which
needs revision.
Mg-Fe in anthophyllite Seifert
265±30
takes place is 425°C.
their crystallization
this possibility
290±20
0.18
(1972) concluded
of cation equilibration
samples were believed
0.36
(425°C) of the sample
no cation migration
which were below T .
425±20
On the basis of this
(Mueller,
at or above 600°C, Ghose and Weidner
the temperature
phyllite
temperature
iron formation
T( 'C)
0.38
at 398°C for 672 hours,
at this temperature.
equilibration
from the metamorphosed
crystallized
[10141]
[118125) was heated
and showed no cation migration result and the observed
[DH7-482]
Maryland [118125]
CoomaComplex, Australia
The cummingtonite
DH7-482
facies)
They carried
out a series of heating
range 400-720°C
at 2 kbar in standard
oxygen
(quartz-fayalite-magnetite
fugacity
of 600°C and above, an equilibrium
a few days.
The exchange
332
reaction
cold-
distribution
can be written
as:
Disordering 050
experiments
k"_I21
:Q,69lI0·6mln-1
kl2:)_4
·O_96dO-'mlo-'
..
LLL'" X 0.45, Ordering
Ie)
experiments
kl2l_4
~ 72
k .. _llJ
"52.
lIO-'min-1 IO-6m1n-1
I
040
10
15
20
Time, doys Figure 5. Changes in the Fe2+ occupancy of the M4site, X~~, in an anthophyllite as a function of run duration at SSQoC, 2 kbar. Opencircles, starting material is natural unheated anthophyllite; closed circles, starting material is anthophyllite previously disordered at 720'C, 2 kbar for 1 day. From Seifert and Virgo (1974).
+ Fe
Mg(Ml,2,3) The equilibrium
(M4) ~ Fe
distribution
define a straight stant exchange
2+
(Ml,2,3) + Mg(M4)
coefficients
line on a ~
reaction
2+
versus
~
found at 600, 670 and 720°C
l/Tk diagram,
indicating
Gibbs free energy ~Go = 4247±54
a con-
cal/mole.
Assuming
the ideal distribution
of Mg and Fe at each set of sites and
assuming
the ~Go to be constant
and the same at lower temperatures,
cation distribution perature
of the unheated
of cation equilibration
anthophyllite
of about 270°C.
ments were made at 500 and 550°C, starting partially
disordered
material
(Mueller,
dt
o
L j=l
the
to a tem-
rate experi-
and previously
The results
presented
for a second-order
in
competing
1967): n-l
n-l C
Detailed
from unheated
(~20°C, 1 day).
Figure 5 can be fitted by the rate equation rate process
corresponds
L
v"k"!jl,,X.(l-X.)-C
where X. = mole fraction
J1 J1 J1 J
1
0 j=l
v ..k ..!jl ..X. (l-X.) , 1J 1J 1J 1
J
2 of Fe + in site i,
1
v .. and v .. = stoichiometric
coefficients,
k .. and k .. = rate constants
for competing
1J
1J
J1
ordering
and disordering
J1
processes, !jl .. and !jl .. = activity 1J
J1
change,
coefficients and
333
for the intracrystalline
ex-
C
=
o
2 total Fe + concentration
In anthophyllite
of all sites per unit cell volume.
there are two M4 and a total of five Ml, M2 and M3 Hence, assuming anthophyllite to be a Mg_Fe2+
sites per formula unit. binary
solid solution,
the above equation
becomes:
dX
4
dt . 2+ 2+ . where X4 and X are mole fractlons Fe I(Fe +Mg) at M4 and Ml,2,3 sltes, 123 respectively. This equation can be reduced to a logarithmic decay for one site occupancy constant
with time (Mueller, 1969) by substituting in the equilibrium Fe 3-4 and the bulk X value and by assuming ideal mixing at
K
12 the sites, namely
=
~123-4
X4(1-X123) X
(1-X4)
123
The rate equation
The disordering
perature
(1969).
=
dependence
a solution
for orthopyroxenes
lX 5
Fe
2
-'5
X
4'
)
equation.
The calculated
that a change of ~: From these kinetic
thermal barrier
(Ghose and Weidner,
1972).
decreasing
rate constant
a heating
there is no evidence
in anthophyllite,
(Virgo and Hafner, Hence,
at lower
more rapidly
for disordering
by 0.001 would require results,
334
are much higher
20 Kcal) by Virgo and Hafner
to drop very rapidly
for ordering
for orthopyroxene
(~55 Kcal) and the tem-
in anthophyllite
(E
for disordering
of four years.
suggested
process
are expected
the rate constant
400°C indicates
tonite
for this differential
of the rate constants
The rate constants
temperature
123
k4-l23 and activation energies determined (1975) at 550°C and 500°C are given in Table 2.
than that for ordering.
viously
[Note that X
k4-l23
energy of the disordering
than those reported
temperatures,
k123-4
rate constants
and Virgo
The activation
1.
now becomes
Mueller (1969) has provided
by Seifert
=
~4-l23
at run
of a high
as was pre-
1969) and cumming-
the degree of ordering
in natural
Table 2. Disordering rate constants k4-l23, where Kfz3-4 = k123-4/k4-123. determined for a natural anthophyllite at 500° and 550°C, and calculated activation energies for disordering, Ean. FromSeifert and Virgo (1975). k4-123 (year-1) 550'C
500'C
EaD (keal)
37.8432 5.0458
3.3112 0.57816
61.6 54.8
Experiments Ordering Disordering
anthophyllite constants.
can be quantitatively At very low temperatures,
due to slow reaction anthophyllite attained
kinetics.
is known,
Seifert
and Virgo
plotted
on a logarithmic
cooling
history
of Seifert
results
derived
indicate
can be calcu-
and time.
indicated
a
(Fig. 6)
Assuming
at 720°C, a
in cummingtonites,
temperatures
an apparent
must either assume
iron formation
of the rocks.
thermal barrier
the relatively
results.
iron formation
ultrabasic
rocks
(425°C)
(1972) are indeed cation equilibration
for the iron formation
of available
it now appears
by the cation distribu-
from metamorphosed
if one assumes no high-temperature
metamorphosed
that are
can be used to derive the
on anthophyllite,
that the low temperatures
tion (425°C)
(unheated)
values
(1977) have presented
and Virgo crystallized
and not crystallization
the basis
the ~:
(T-T-T) diagram
and 265°C) and one from a metamorphosed
present
of a natural
rate of 2.5 x 10-5°C/yr for the rock can be derived.
studied by Ghose. and Weidner peratures
rate
process will cease,
at a given temperature
time scale, which
tion in two cummingtonites (290
the ~:
transformation
In view of the kinetic
0
Provided
of a rock in terms of temperature
that the anthophyllite
very likely
the ordering
(1975) and Seifert
time-temperature-(percentage)
cooling
in terms of measured
from these rate constants
after a given time interval
lated.
linear
interpreted
However,
to cation order to be
high temperature
cummingtonite
of equilibra-
cannot be explained
In fact, all of the samples
equilibration
temperature
fast or that the rate constants
siderably
different
is rather
unlikely
(1971)
of 425°C or higher.
rate for these cummingtonites
unusually
of cummingtonites
from those of anthophyllites.
on
from the
of Quebec studied by Hafner and Ghose
that the cooling
tem-
One was
are con-
The latter possibility
in view of the fact that samples 118125 and DH7-482 Fe (Table I) have very similar x values (0.364 and 0.378) and yet indicate
very different
temperatures
of cation
335
equilibration
(290 and 425°C).
1.0
I ~ ~
,.
!
.:.
uu 0 + N
•
~
LL
O.S
...•......
I
.....
:"
•. ..ti-
..... .
'
..•... o
Figure 7. Distribution of Fe2+ and Mgin Ml and M3 sites of 28 blue sodic amphiboles; the dotted line corresponds to the ideal solution mode L at each site, where Kn =
2+ Fe oee.
(M3)
~(1-X;;;)/~(1-~) Ungaretti
o
0.5
We urgently anomalies
Mg-Fe
need kinetic
Ganguly
From
1.0
studies
so that eventually
of rocks.
: 0.403.
(1980).
on cummingtonites
to clarify
these
they can be used to determine
cooling
(1982) are currently
this problem.
and Ghose
studying
rates
in sodic amphiboles In the sodic amphiboles,
M2 site is occupied Chose, sites. crystal
by trivalent
MM.
1965). The Fe and Mg 2 Fe + shows a preference structure
1968; Bancroft series,
where
refinement
and Burns,
the Mossbauer
tive enrichment (Bancroft
relatively relatively distribution indicating
for M3 in glaucophane,
and Mossbauer
1969).
spectroscopy
1949;
In the Ml and M3 as indicated
by
(Papike and Clark,
In the glaucophane-crossite-riebeckite
and infrared
1969).
by Na+, the
ions such as Al and Fe (Whittaker, ions are concentrated
spectra
indicate
a change in the rela-
of Fe2+ ions from M3 to Ml with increasing
and Burns,
have determined
the M4 site is occupied
Ungaretti
Fe3+ content
et al. (1978) and Ungaretti
(1980)
cation distributions
in 26 blue sodic amphiboles that are poor in ferric iron. The Fe2+ in these amphiboles shows a strong preference for the M3 site; in addition, the Fe2+_Mg2+ between
Ml and M3 sites shows a smooth hyperbolic pattern, an ideal distribution of Fe2+ and Mg at each site (Fig. 7).
The equilibrium
constant, (1 -
Fe XM3)
(1 -
Fe) XMl
0.403
337
•
If we assume
the temperature
equilibration
we obtain an estimate reaction
of crystallization
of these sodic amphiboles
of the Gibbs free energy,
The P211m
7
C21m phase transition
showed that the exsolved
by other clinoamphiboles. identified
ultrabasic
(Mg,Fe) cummingtonites,
X-ray studies
transforms
indicated
double silicate
because
of the high
structural
composition chains,
are brought
7
purely displacive
cummingtonite
no chemical
in the P21/m
phase, which
338
in
to the
the transition
in being
the P21/m cummingof the more stable
Apparently,
forms instead
in
both
C2/m transition
bonds are broken,
(Sueno et al., 1972).
are similar.
of tetrahedra
temperature,
In contrast 7
In both
or differences
about by the rotation
identical.
above
of the high-tempera-
(Sueno et al., 1972).
due to temperature
C2/c transition,
tonite is a metastable
structure
so that above the transition
manganoan
cummingtonite
of the Ml, M2, M3 and M4 octahedra changes
crystallographically
magnesiocurnmingtonite,
that this primitive
to another manganoan
at room temperature
forms, the configurations
P21/c
to that found in other, C-
to C-centered
The crystal
ture form at 100°C is very similar that is C-centered
pigeonite
by Papike et al. (1969);
i.e., four short oxygen bonds at an
reversibly
40°C (Prewitt et al., 1970).
chains become
(CaO.36NaO.06MnO.96
of 2.lS4A and two further ones at 2.Sll and 2.6S0A.
High-temperature
the silicate
of a primitive
distinct
However,
of this site is comparable
distance
The principal
composition
has been determined
of kinking.
shown
of the M4 site (0.49 Mn, 0.28 Mg, 0.19 Ca, 0.03 Na, 0.01 Fe),
the configuration
cummingtonite
in tre-
(Ross et al., 1969;
rocks
The crystal structure
with the chemical
degrees
cummingtonite
cummingtoni te has since been
by two crystallographically
chains with different Mn occupancy
(196S) who first
rather than the usual C2/m symmetry
MgS.S7FeO.OlAlO.Ol)Si8022(OH)2 it is characterized
It was Bown
Such "primitive"
in many metamorphosed
cummingtonite
cummingtonite
of magnesium-rich
Kisch, 1969; Rice et al., 1974). manganoan
AMPHIBOLES
in magnesium-rich
lamellae
P21/m symmetry,
molite possess
chemical
~Go, of the ion-exchange
IN FERROMAGNESIAN
Nature of the structural changes.
centered
of
to be about 1.09 Kcal/mole.
PHASE TRANSITIONS
average
and the temperature
to be about the same (~300°C),
orthorhombic clino
(anthophyllite)
phase, due to the sluggishness
ortho transformation,
+
siderable
breakage
The chemical is known
mination
of a primitive (specimen
compositions.
distances
with four oxygen
atom at 2.4lSA;
These new data further
with
into primitive
that domains
of P-cummingtonite
relationships
with one another
phase domains
in pigeonite,
In principle, when
1974).
(h + k
= 2n +
using the dark-field
are usually
(Ross et al., 1969).
the degree of sharpness domains which
it is expected
The formation photographs
1), which violate
these reflections
technique.
of the
by the
to view the anti-phase
is imaged through
1) on the hOl net of primitive
Montana,
When C-centered
for a review of anti-
in X-ray diffraction
it is possible
the crystal
microscope,
= 2n +
anti-phase
is
will form which will have anti-phase
(cf. pigeonite;
of extra reflections
centering.
diffuse
cummingtonite
cummingtonite,
see Morimoto,
phase is expressed
Mountain,
oxygen atoms are at
the idea that the P2 /m 1
support
transforms
(h + k
of 2.070A, with
phase.
cummingtonite
electron
distance
the sixth and seventh
domains in cummingtonite.
directly,
86 mole % of the Mg
(Ghose and Wan, 1981; in preparation).
anti-phase
appearance
deter-
(Finger, 1970), i.e., it is five-
Possible
primitive
structure
Switzerland,
atoms at an average
of 2.868 and 2.889A
a metastable
con-
Rice et al., 1974) indiof the M4 site (highly enriched in Fe2+) is
cates that the configuration
a fifth oxygen
The crystal
(Mg,Fe) cummingtonite
#3lB, Ticino,
close to that found in anthophyllite coordinated
and involves
range of the P2 /m (Mg,Fe) cummingtonite 1 from 77 mole % of the Mg component (Ghose, 1974, un-
to more magnesian
component
is reconstructive of M-O bonds.
composition
to extend
published)
which
and reformation
of the
the Cdomains in the
The reflections
cummingtonite
from Ruby
sharp but in some cases may be weak and By analogy with pigeonite,
of these reflections are present
indicates
in primitive
we postulate
that
the size of the
cummingtonite
(cf.
Hamil et al., 1973, and Ghose et al., 1972). Although tonite,
anti-phase
attempts
transmission
electron
1972, unpublished;
domains
probably
to image the anti-phase microscopy
exist in primitive domain boundaries
cummingdirectly
by
have failed so far (Lally and Ghose,
G. L. Nord, Jr., 1973, unpublished
for the failure may lie in the low transition 339
results).
temperature
The reason
(~lOO°C)
for
P
+
C cummingtonite;
presumably
beam to a temperature domains.
However,
higher
if this explanation
private communication), disappearing
the sample heats up under the electron
than Tc' thus obliterating
is true, according
diffraction
the thin foil, since only the position
As a matter of fact, no h + k
diffraction
pattern,
Whether
i
i
about
under observation
2n spots can be found in the
except a diffuse streak in the overexposed
up of the specimen may not be a satisfactory
anti-phase
(1981,
2n spots
pattern while moving
of the specimen
is heated.
Hence, heating
to Nord
expect to see some h + k
one would
from the electron
the anti-phase
domains exist in primitive
pattern.
explanation.
cummingtonite
is still un-
certain. Anthophyllite-cummingtonite
phase relations
By analogy with pyroxene observed
exsolution
centered
inversion
phase relations
phenomena
in cummingtonites
in magnesium-rich
primitive
and C-centered
with respect
calcic clinoamphibole
field of anthophyllite.
inversion
P21/m cummingtonite as a metastable
to anthophyllite,
is prevented proceeds";
The rest of the sequence cummingtonite
intergrown
reconstruction
and a displacive
the primitive
should occur
of the crystal
transformation
cummingtonite
and inversion
may persist
from the Gouverneur,
phases:
(space group P21/m);
New York se-
complete
to anthophyllite."
in this scheme has now been found in the
Mg-rich
Switzerland
primitive
of anthophyllite
precession
to
rich, may show part of the reaction
from Ticino,
is primarily
with fine lamellae Single-crystal
in the stability
above, but the reaction has stopped well before
unmixing of the Ca-component
The amphibole
on cooling unmixes
to anthophyllite
"The cummingtonites
area, which are very magnesium
primitive
among
"A C2/m am-
to place its composition
Recrystallization
phase.
quence described
phase relations
and anthophyllite:
but since this would require a complete structure,
Ross et al. (1969)
Ca and Mg (or Fe2+) in the M4 site, which is stable
at high temperature sufficient
the following
cummingtonite
to C-
and the primitive
cummingtonites,
and Prewitt et al. (1970) postulated
phibole containing
and on the basis of the
parallel
photographs
(Evans et al., 1974).
cummingtonite
(86 mole % Mg),
to the (010) and (100) planes.
of the hOZ net indicate
three oriented
(1) the bulk of the crystal consists of cummingtonite (2) a small amount of anthophyllite
340
(space group Pnma)
the a* axis with the cummingtonite;
sharing
(space group C2/m) sharing
(~5%) of tremolite mingtonite. tively
and (3) a very small amount
Hence,
the anthophyllite
the a* axis with
and tremolite
the cum-
phases have respec-
(100) and (101) planes in common with the cummingtonite.
situation
is completely
analogous
to the inversion
studied by Ghose et al. (1973), in which lamellae
situation,
we conclude
tremolite, Strictly course,
to the orthorhombic
it is not possible
evidence
indicates
The indirect
relationship
to determine
augite
to orthopyroxene
first exsolved
anthophyllite
phase.
of these three phases,
the direction
is the low-temperature that the anthophyllite
exsolved
By analogy with this
that the Ticino cummingtonite
and then inverted
which
inverted
the host pigeonite.
from the orientation
and determine
of a lunar pigeonite
the pigeonite
to (001) and subsequently
parallel
the (100) plane with
sharing
This
phase.
of
of this reaction
However,
the indirect
is the low-temperature
phase.
evidence
includes
the fact that the anthophyllite
has diffuse
X-ray spots elongated
parallel
to a*,
of very
fine anthophyllite
lamellae
parallel
a few hundredXngstromsthick. tonite, which
which
is retrograde.
one concludes inversion
the presence
to (100), which
Secondly,
is monoclinic,
than anthophyllite, observing
indicating
are at the most only
it is well known that the cumming-
can accommodate
is orthorhombic.
more calcium Hence,
in the structure
the reaction
In this case, from other geological
that a fluid phase was present,
we are
evidence
which may have made the
possible.
MISCIBILITY
GAPS AND EXSOLUTION
TEXTURES
IN AMPHIBOLES
Introduction Many compositionally under equilibrium phases. below
complex
conditions
The attainment
considerably,
rates of the exchanging
detection solution
application
cations.
equilibrium
however,
As a result,
at low temperatures
of exsolution lamellae
of techniques
to break
extremely
simpler
at temperatures
even if an amphibole a two-phase
optically,
that
assemblage,
because
fine and submicroscopic.
that are capable of a resolution
341
down
by the slow diffusion
is effectively
may be very difficult
are commonly
are expected
into two or more compositionally
of thermodynamic
SOO°C is hindered
has equilibrated
amphiboles
better
the exHence, than
that possible
with optical microscopy,
fraction
or electron
analysis
using energy dispersive
exsolution.
diffraction
Fine-scale
is the most reliable
appropriate
kinetics,
lamellar
amphibole
pairs.
of equilibrium
two of which have been further of the subsolidus clude:
reactions
from observed
exsolution
by experimental
in the laboratory.
in
tremolite
although
miscibility
not yet confirmed,
likely on crystal-chemical
cummingtonite-
In addition,
gaps between
actinolite-glaucoare very
grounds. pairs with corresponding
crystal-chemical
Immiscibility
under the following
determinations
and cummingtonite-riebeckite
of the amphibole
us to draw some general
phenomena,
(actinolite)-riebeckite,
and richterite-riebeckite.
hornblende-glaucophane
gaps between
These pairs in-
cummingtonite-actinolite,
actinolite-hornblende,
in amphiboles.
time period
have been achieved,
a number of miscibility
confirmed
phase relations
anthophyllite-gedrite,
Analogy
of slow reaction
a reasonable
arfvedsonite-cummingtonite,
phane,
phase relations
results may be suspect.
pairs have been confirmed
hornblende,
These results
of subsolidus
within
to observe
of two amphiboles
in amphiboles.
unless reversed
X-ray dif-
with chemical
may be necessary
Again, because
In spite of these difficulties, amphibole
combined
intergrowth
by the determination
is hampered;
such experimental
detection,
proof of exsolution
attainment
the laboratory
and microscopy
oriented
should be corroborated between
such as single-crystal
pyroxenes
rules with respect
is to be expected between
allows
to exsolution
two amphiboles
conditions:
Rule (1): where the M4 site is filled with large cations such as Ca2+ in one amphibole and small cations such as Fe2+ and Mg2+ in the other Rule (2):
(hornblende-cummingtonite, where
the A-site
and empty in the other tonite, Rule
the other Hence, the A-sites
(hornblende-actinolite,
gedrite-anthophyllite,
(3):
where
actinolite-cummingtonite);
is fully or partially
occupied
in one
hornblende-cumming-
richterite-riebeckite);
the M4 site is occupied by Ca in one and by Na in
(actinolite-riebeckite).
the size and the charge of the cations play critical
boles such as glaucophane
roles.
occupying
the M4 and
On the other hand, between
two amphi-
and riebeckite,
342
no miscibility
gap is to be
expected
except under very low-temperature
conditions (below perhaps cations involved (A13+ and Fe3+ in the M2
300°C), since the exchanging
site) have similar charges and ionic radii. chemical
complexity
emerging
in terms of miscibility
confirmed
of the amphiboles,
in judiciously
a generally
needed both on natural assemblages
and synthetic
Sundius
cummingtonite-grunerite
Non-existence
the existence
of miscibility
and (d) exsolution primary phase.
overgrowth
can be sometimes and exsolution
X-ray investigation.
amphibole pairs Provided
However,
establishing
it can
such pairs prove chemical equi-
since such pairs often appear as intergrowths,
homogeneous
tergrowth
these three of miscibility
(see Klein, 1968).
of two amphibole
of one amphibole by another,
on another,
between
has been established,
gaps.
series,
gaps among these
number of analyzed
which can be (a) primary intergrowths placement
and tremolite-actinolite
compositions
in the literature
be shown that chemical equilibrium
librium can be difficult,
for members of the antho-
proof of the existence
Since then, a considerable
have been reported
systems to clarify the
the miscibility
of amphibole
series was taken as the indirect gaps.
much work is still
in amphiboles.
(1933) was able to outline
series.
picture is
can be experimentally
Obviously,
On the basis of a large number of analyses phyllite-gedrite,
consistent
gaps, many of which
chosen systems.
sub solidus phase relations
In spite of the perplexing
(c) overgrowth
phases,
of one amphibole
or unmixing of two amphiboles
Replacement
(b) re-
from a
of one amphibole by another and
recognized.
Distinction
cannot be made without
In clinoamphiboles,
between primary
detailed
in-
single-crystal
the host and the exsolved
phases usually share the (101) and (100) planes in the space group C2/m. In the I2/m orientation, clinopyroxenes,
which
these lamellae
corresponds are parallel
of
to the (001) and (100) planes
to Fig. 26 in chapter by Robinson et al., p. 56, Vol. 9B).
(Fig. 8--refer
For further discussion we will exclusively clinoamphiboles.
Very fine-scale
crystal X-ray diffraction miscibility
to the C2/c orientation
use the C2/m orientation
exsolution,
and electron
as observed
microscopy,
for
through single-
is a clear proof of
gaps in amphiboles.
Unmixing
of two amphiboles
proceed by two mechanisms: decomposition.
from a primary homogeneous
(1) nucleation
In the latter mechanism,
343
phase can
and growth; or (2) spinodal
compositional
waves are set up
within
the homogeneous
compositional solution
modulations
lamellae.
mechanism,
phase in the initial subsequently
Nucleation
but the spinodal
stages of exsolution.
develop
as regularly
and growth appears
mechanism
These
spaced ex-
to be the most common
seems to operate
in some cases
(e.g., gedrite-anthophyllite). Actinolite-hornblende Shid8 and Miyashiro tinolite
(1959) reported
and blue-green
the Central Abukuma temperature
hornblende
Plateau,
from
sharp boundaries
to indicate
an equilibrium
occurrences
from metamorphic
of hornblende
in actinolite
these two amphiboles arrested
shire
1978).
(Brady, 1974).
woven.
where
Klein
parallel
lamellae
igneous
of hornblende
intergrowths
gap.
Cascades,
(1969) described
of actinolite
(Grapes, 1975; Grapes
in apparent
chemical
at Hanover,
equi-
New Hamp-
a rock from Tsintobolovolo,
exsolution
are inter-
lamellae
analyses
(1970) observed
Tagiri
0.25 µm
exsolution
(1977) suggested
and hornblende
an equilibrium
assemblage
of tremolites
that the
in some metamorphosed which may indicate
gap is also suggested
a
by the composi-
and aluminous
hornblendes
from
facies rocks from the North
(Misch and Rice, 1975).
Oba (1980) has experimentally tremolite-pargasite
evidence,
but represent
and vice versa from metamorphosed
New Zealand.
range of the amphibolite
Washington
zones and patches
grains of the two amphiboles
shows abundant
A miscibility
tional gap between the lower medium
and hornblende
in actinolite
rocks represent
miscibility
actinolite-
From the textural
during recrystallization
Cooper and Lovering
rocks of southern
lamellar
were
to (101) and (100), which are most likely actino-
lite in composition.
basic
Numerous
grains show irregular
equidimensional
grains
rocks have since been described
grains in amphibolites
The green hornblende
in thickness
assemblage.
and vice versa.
Actinolite
occur as separate
Madagascar,
actinolite
with
of two amphiboles
are most likely not in equilibrium,
stages of reaction
and Graham, librium
subhedral
ac-
in the lowest
The two amphiboles
intergrowths
considered
1969) where
basic rocks from
crystallized
zoned crystals,
and fibrous
hornblende (see Klein,
metamorphosed
facies.
in discontinuously patches,
gap between
Japan, which
range of the amphibolite
with hornblende
a miscibility
determined
join in the temperature
344
the phase relations range 750-ll50°C
on the
under water
ot
1000
1 kbor
950
900
o
:-' ~ 850
~
Por q-v
0
~ 800 c. E >750
.0
~
:
{',
.v
---- -A -- --- 9' ----- --- ---_4 - - - -- - -- -- -- - - - - - - ~- - - -- ~- - - -I
700
e
8·
l
20
40
60
vapor pressures
of 1 and S kbar.
solid solution
between
100
80
mot.
.,.-+
Po
At 8S0°C and S kbar,
the composition
(Fig. 9).
Under
these conditions
litic and pargasitic to be in agreement from skarns
amphiboles
lS tremolite
=
tremolite,
system show the existence from igneous 1 kbar)
(low pressure Ts
and TrOPa
' lOO and pargasite
Pa and Tr Pa tremo90 lO lO 90 coexist with vapor. These results seem
with field relations.
and marbles
(Tr
between
there is a con-
Tr8SPa
At 800°C and 1 kbar, there is a solvus between
Tr-Ts-Ha
Figure 9. Solvus between tremolite and pargasite at 1 kbar. From Oba (1980).
, .v
0 Tr
tinuous
Cp~.Fo
~.PI.MO
Tr
Plots of amphibole
and high temperature)
tschermakite,
of a compositional
Ha
within
hastingsite)
gap, whereas
rocks formed at high temperature
do not show the compositional
=
compositions the
ternary
amphiboles
and high pressure
(above
gap (Oba, 1980).
Hornblende-anthophyllite Sundius
(1933) postulated
anthophyllite, ever, exsolution same crystal blage
in such systems
system.
gap between
and an orthorhombic
hornblende
amphibole.
is always of a second amphibole
For example,
from New Hampshire,
parallel
a miscibility
i.e., a monoclinic
in a hornblende-anthophyllite
the hornblende
exsolves
primitive
to (101) and (100), and the anthophyllite
exsolves
1969; Ross et al., 1969).
(Robinson
and Jaffe,
explained
on the basis of crystal
on the nucleated orthopyroxene,
phases.
where
structural
The comparable
augite may exsolve
345
assem-
gedrite can be
exerted by the host
analog in pyroxenes metastable
of the
cummingtonite
These phenomena
control
and How-
pigeonite
is augitealong
(001).
The hornblendes
coexisting
coexisting
cummingtonite
with
hornblendes
coexisting
cummingtonite,
with anthophyllite (Robinson
hornblendes
cummingtonite.
Actinolite
(tremolite)-anthophyllite (1968) has analyzed
anthophyllite
above.
Island, Arctic Canada.
ultramafic
Buseck
composite
(1980) describe amphibole
The intermediate
contact.
(anthophyllite)
cummingtonite
and actinolite lamellae
The calcic amphiboles
(hornblende
A similar Mg-Fe
distribution
pyroxene-calcic
pyroxene
crystals
features.
Veblen and
consisting
of low
at the other.
consist of a fine inter(100).
The actinolite
on (101). have higher Mgl
or actinolite)
that coexists with them (Klein, 1968).
is found in igneous
pairs
Vermont,
crystals
on planes
exsolved
than anthophyllite
All three amphi-
at one end and actinolite
parts of such composite
growth of anthophyllite
ultramafic occur as in-
exsolution
body at Chester, amphibole
and
assemblage
from metamorphosed
and devoid of any microscopic
From the metamorphosed
exsolve
pair described
All three amphiboles
grains and with all three in mutual
(Mg+Fe) ratios
primitive
This pair has a distinctly
ratio than the hornblende-anthophyllite
boles are homogeneous
contains
exsolve
cummingtonite
tremolite-actinolite
New York.
of actinolite-cummingtonite-anthophyllite rocks of Baffin
calcium
Furthe~ore,
et al. (1980) have described an equilibrium
Kamineni
dependent
with
the coexisting
(+ talc) from Balmat,
higher Mg/(Mg+Fe)
generally
coexisting
C-centered
Klein
and Jaffe, 1969).
with anthophyllite
whereas
have less iron than those
(Kretz, 1963).
and metamorphic
ortho-
These observations
can be
explained
by the fact that the M4 site in anthophyllite and the M2 site 2 in orthopyroxene strongly prefer Fe +, whereas these sites in calcic amphiboles and pyroxenes are occupied by Ca2+. Hornblende-cummingtonite Although
Eskola
(1914) first noticed
hornblende-cummingtonite
growths which may have been due to unmixing, to replacement suggested
of hornblende
an exsolution
and proposed
by cummingtonite.
was subsequently
and single-crystal
Asklund
them to be due
(1923) first
origin of the hornblende-cummingtonite
that a miscibility
This suggestion
he interpreted
gap exists between verified
X-ray diffraction
346
intergrowth
these two amphiboles.
by detailed
studies
inter-
optical
of coexisting
microscopy
hornblende
and
cummingtonite
from amphibolite
fine (101) lamellae
rocks at Skothagen,
of cummingtonite
Sweden, which
in the hornblende
and vice versa
(Asklund et al., 1962).
Similar
exsolution
blende
observed
through
optical microscopy
rocks in Pernio,
Finland
(Seitasaari,
and cummingtonite
from amphibolite Australia
lamellae
1962), Orange, Massachusetts,
(Vernon,
son, 1963), New South Wales, Australia
in coexisting
horn-
were reported
1952), Queensland,
and New Hampshire
(Binns, 1965), Novarra,
1965), and Adamello,
(Boriano and Minutti,
revealed
Italy
(Robin-
Italy
1966), and
(Calleghari,
other areas. to the (101) lamellae,
In addition and cummingtonite fraction
were noticed
cummingtonite
intergrowths microprobe
(1969) and Robinson for details. unit-cell
contains
have been extensively
analysis
We summarize
indicating
the structural
than the (100) lamellae.
with anthophyllite tonite;
contain
furthermore,
of gedrite
(Robinson
coexisting
lamellae control
and grunerite
hornblende
contains
lamellae
are usually
thicker
may subsequently Hornblendes
less iron than those associated anthophyllite
with transmission
coherent
lamellae
to (100) and (101), which nucleated
parallel
are P-cumming-
of the host and the metastable
Gittos et al. (1974, 1976) have studied
heterogeneously
to (100) and (101).
have nucleated
with C-cummingtonite
in hornblende
recrystallization.
the coexisting
that
be
coexisting with cumming-
shows exsolution
lamellae
and Jaffe, ,1969).
hornblende
also contains
specimens
but when it is coexisting
The (101) lamellae
The exsolution
by intergranular
Table 3 shows
and cummingtonite
of C-cummingtonite,
the exsolution
nature of the P-cummingtonite.
obliterated
(1969). These papers should be consulted
The hornblende
lamellae
using optical
by Ross et al.
here some Df their results.
phenomena.
exsolution
and actinolite-
studied
and X-ray diffraction
of 10 hornblende
with anthophyllite, tonite,
1966; Jaffe et al.,
hornblende-anthophyllite
and Jaffe
dimensions
show exsolution
in hornblende
and X-ray dif-
et al., 1969).
Hornblende-cummingtonite,
microscopy,
fine (100) lamellae optical microscopy
1963; Binns, 1965; Calleghari,
(Rbbinson,
1968; Robinson
through
exsolution
electron
of grunerite
Figure
of grunerite.
parallel
In turn, the grunerite
of hornblende
10 shows hornblende
at a (100) twin boundary
347
lamellae
of
The
approximately
heterogeneously.
nucleated
intergrowths
microscopy.
approximately
lamellae
that
The semi-coherent
Table 3. Crystallographic data for amphiboles showing exsolu~ion, from metamorphosed volcanics from Massachusetts and New Hampshire (Ross et aZ., 1969).
No.
Crystal No.
%01 grain
Amphibole Intergrowths
brA)
Space Group
cIA)
----~'----'----~------,---~,----~'----I-
6A9X
hornblende host P-cummingtonite P-cummingtonite anthophyllite gedrite
,_---.----~,
90 7 3
on (100) on (TOl)
host
I
----1---'
N30X
anthophyllite gedrite
host
hornblende host P-cummingtonite P-cummingtonite
----,
on (T01) on (100)
--I C-cummingtonite hornblende host C-cummingtonite
on (100)
---1--1
4
9.81 9.49 9.49
18.02 18.02 18.02
5.31 5.30 5.30
100
9.50
18.18
99 1
9.77 9.51
18.02 18.02
on (T01)
90 10
hornblende host C-cummingtonite C-cummingtonite
on (100) on (T01)
94 3 3
9.51 9.82
18.15 18.15
9.82 9.51
18.12 18.12
W95JX
gedrite host anthophyllite
17.81
1753.5 1773.1
105°0' 101°55' 102°5'
C2/", P2,/", P2,/m
906.7 886.8 886.3
5.31
101°55'
C2/m
897.3
5.32 5.30
104°40' 102°5'
C2/m C2/m
906.1 888.1
18.601(4)"117.839(3) 18.56 18.56
17.87 18.11
1754.5 1778.1
80 20
18.54 18.54
17.76 17.98
5.27 5.27
PnlJl1. Pnma
1735.2 1756.8
9.49 9.80
18.13 18.13
1--,---1--_,
18.08 18.08
5.31 5.31
55 45
118.58 18.58
118.11 17.85
5.28 5.28
75 25
I
9.79 9.48
118.02 18.02
5.31 5.31
85 15
9.45 9.75
I
I
18.00 118.00
5.30 5.30
80 20
118.57 i 18.57
2-A
anthophyllite gedrite
host
_
1746.8
Pnma Pnma
9.80 9.52
!
~I
5.29 5.29
85 10 5
I
Pnma
913.0 897.8
1753.2(5)
hornblende host C-cummingtonite on (100) cummingtonite on (T01)
P-cummingtonite host hornblende on (100)
C2/", C2/m C2/1Il
Pnllla
98 2
1-P
__ I
15.284(2)
C-cummingtonite host hornblende on (100)
ho~---II P-cummingtonite on (100)
104°55' 102°10'
I---'--I---I~---I---
80 20
C-A
QB2K:--Il-H-II::blende
_
896.2 918.3
C2/m C2/m C2/m
5.29
90 6 4
.
102°5' 104°50'
5.31 5.33
C-cummingtonite host hornblende on (100) hornblende on (TOl)
I'
__'
_
I--~
5.31 5.33
A
host
'----1--
1---1--1---1----1--100
1---1----1
anthophyllite gedrite
1773.1 1756.4
Pnma Pnma
'-----,---~I---
18.55 4.58
>99