360 12 161MB
English Pages 373 Year 1983
Table of contents :
Page 1
Titles
REVIEWS In
(Formerly: "Short Course Notes")
Volume 2
SECOND EDITION
FELDSPAR MINERALOGY
The Authors
MINERALOGICAL SOCIETY OF AMERICA
REV002copyright.pdf
Page 1
Tables
Table 1
Page 1
Titles
FELDSPAR MINERALOGY
FOREWORD TO THE SECOND EDITION
iii
REV002ACKN.pdf
Page 1
Titles
ACKNOWLEDGMENTS
SELECTED REFERENCE WORKS
Page 1
Titles
FELDSPAR MINERALOGY
TABLE of CONTENTS
CHAPTER 1.
P.H. RIBBE
The CHEMISTRY, STRUCTURE and NOMENCLATURE of FELDSPARS
CHAPTER 2.
ALUMINUM-SILICON ORDER in FELDSPARS:
DOMAIN TEXTURES and DIFFRACTION PATTERNS
P.H. RIBBE
Page 2
Titles
The preeession method 32
The oseillation method 32
Peristerites
Bytownite
High plagioelases
'e '-plagioelase
CHAPTER 3.
H. KROLL & P.H. RIBBE
LATTICE PARAMETERS, COMPOSITION and Al,Si ORDER in ALKALI FELDSPARS
vi
Page 3
Titles
CHAPTER 4.
LATTICE PARAMETERS and DETERMINATIVE METHODS
CHAPTER 5.
D.B. STEWART & P.H. RIBBE
Tables
Table 1
Page 4
Titles
CHAPTER 6.
R.A. YUND & J. TULLIS
SUB SOLIDUS PHASE RELATIONS in the ALKALI FELDSPARS
CHAPTER 7.
R.A. YUND
MICROSTRUCTURE, KINETICS and MECHANISMS of ALKALI FELDSPAR EXSOLUTION
Page 5
Titles
CHAPTER 8.
DIFFUSION in FELDSPARS
R.A. YUND
CHAPTER 9.
PHASE EQUILIBRIA of PLAGIOCLASE
Tables
Table 1
Page 6
Titles
CHAPTER 10. P.H. RIBBE
EXSOLUTION TEXTURES in TERNARY and PLAGIOCLASE FELDSPARS;
CHAPTER 11.
A.M. HOFMEISTER & G.R. ROSSMAN
CHAPTER 12.
SOME CHEMICAL PROPERTIES of FELDSPARS
Tables
Table 1
Page 7
Titles
CHAPTER 12, continued
CHAPTER 13.
DEFORMATION of FELDSPARS
J. TULLIS
Page 8
Titles
CHAPTER 13, continued
APPENDIX: INDEXING FELDSPAR POWDER PATTERNS
Page 1
Titles
Chapter 1
CHEMISTRY, STRUCTURE and NOMENCLATURE of FELDSPARS
Tables
Table 1
Page 2
Titles
tP
i;j
ALKALI
FELDSPARS
Page 3
Titles
Four- membered tetrahedral ring
- .f,zl'a
- ()
Actual
n
Stylized
Page 4
Titles
a
__ 1
Page 5
Titles
Ie Id spar
gismondine
[lTOI
[110J
5
Tables
Table 1
Page 6
Page 7
Page 8
Titles
T
1
c'
block - - four -fold
\. ~~' (e) Feldspar building
)
//1/'
+ // (b) Two views of crankshaft linkage of four-membered rings
Page 9
Tables
Table 1
Page 10
Page 11
Titles
T2mc
Page 12
Page 13
Titles
C2Im
o
Sonidine
T,
z
I
~/
13
Tables
Table 1
Page 14
Page 15
Titles
o.
c.
pi
Page 16
Titles
PI
Page 17
Tables
Table 1
Page 18
Tables
Table 1
Page 19
Titles
I - anorthite
Page 20
Page 1
Page 2
Page 3
Titles
HIGH I
j SANIDINE
LOW
Mean T -0 distance, A
~
Approximate AI content of T site
I
.:
I
Tim
DI TlmcC; "e,C:
I / I
(i) MONOCLINIC HOST
(ii)
(iii)
(iv)
(v)
ttO = t1m = t.oc = time
Page 4
Page 5
Titles
20 h .
25
Tables
Table 1
Page 6
Page 7
Tables
Table 1
Page 8
Page 9
Titles
c
900
p
i1
Ii [At/IAt-Si)l
29
Page 10
REV002C002_p31-55.pdf
Page 1
Page 2
Titles
The precession method.
The oscillation method.
Page 3
Titles
33
Tables
Table 1
Page 4
Titles
• f
e
1--------+----
"c I •
e
c !J
o
21
022
012
002
b* -d
P-anorthite
T - anorthi te
Huttenlocher
'e' - plcq, (An65)
001 O~
,a Q
e
,e
020
Beggild (Ansa)
'e' - plag. (An30)
Peristerite
Albite
S --I __ --
e __ ::: = ::-:3 ----
-----..,__--
c ----:;mrll I
- --- d
mol % anorthite
--1---
s -
100
*
bl,2
80
60
40
g
20
o
* 0*
01 __ 2====
34
Tables
Table 1
Table 2
Page 5
Tables
Table 1
Page 6
Page 7
Titles
~ ~
Page 8
Titles
c*
~
ffimffmmR
I 1 I
I I 1
o.!o.o.o.lo.o.o.p-; If
. /.0.0.0.1.0.0.0./. ' ..•.
38
Page 9
Titles
b
a
Tables
Table 1
Page 10
Titles
Albite.
40
Page 11
Titles
Peristerites.
Page 12
Page 13
Titles
1,75 rr----,-----,-----,,-----,------,--,-----,----,-----,-----,-,
1,70
a.
o.
'tJ co ....
a. co
I U co
>- U
c: rl
ro m ...... m
rn .. c "C
o rn ~ m
rn a 0 U) 0
U a. r.... to
en ........ k tU
CD r-4 m u
m c:
....
L-' Q)
"
I~
60
Page 5
Titles
'" ~
~u,
"''''
"''''
-
c- -sr \0 -a
r--O r--O
......
oco ca e- 0('-
0\ ro en CO C1\ rn
cc
•
-
u a •• V
65
Page 10
Titles
......
e- n ..... t") Nt")
'"
•
>-
If)..;;t am N.;;;t 000 moo com om Nn LnN D-=:t
....................
"'N
"
. ...
-e
"
. ...
"'N
o
~
"
....
o
"
....
o
....
"
. ...
""
'"
"
~ ~'"
'"
"
....
"'N
"''''
....
'"
"
..,
"''''
'"
"
....
"
"''''
a.
s-:
"
"
....
'"
o
....
"'N
"''''
'"
a.
'"
"
....
'"
"
....
"
~I E
'" "
u,
"
"
~I NO
,
•
..
+ //1
Vo I u me ij.i
.1/
tl.!,
»»
I . "'l"
.-./ "
j'
..
c
E
>
Mol % Or
Page 17
Titles
94.00
93.0·
92.0·1-
a,y
91.0·
\
r
a
-
-
-
90.0·
89.0·
88.0·
r
• • • y
o_o_._'_._._._.. . . .. to _!._._+.
__L_._ I , I , I ·-:-T-~-·,-:-1-~~·LA-L"1
__ L, 1 ' I ,
Ab 20 40 60 80 Or
73
Page 18
Page 19
Titles
Z r
Page 20
Tables
Table 1
Page 21
Page 22
Titles
12.76
o
12.80
12.84
12.88
1292
12.95
13.00
13.04
Tables
Table 1
Table 2
Page 23
Page 24
Titles
*
;..... 90.0°
89.0°
88.0°
AA
86.0°
87.0°
88.0°
89.0°
90.0°
Page 25
Page 26
Page 27
Titles
.,
oL _
~
83
Tables
Table 1
Table 2
Page 28
Tables
Table 1
Page 29
Page 30
Page 31
Titles
7.90.
785
·~78o.
=
.-
='
~775
- .
770.
~~~M':::.:line
• ~.7.9189~03361 t,m
\. tr1To.=785o.8-o..1548 ·t)
Sonidine "e., ~ L
~:, ..... "Irthoctoses"
.~
,
trllo. = 7.8919 -0..2626· t.o
Low ~pop,
765
0.
0..2
0..4
0.6
0.8
1.0.
Page 32
Tables
Table 1
Table 2
Page 33
Page 34
Titles
710
720
90
Tables
Table 1
Table 2
Page 35
Page 36
Titles
Table 6. Equations and coefficients to calculate from tr[110], [110] (10
'-
-- 0.20
0«
,~
,
0.00
0.10
COEFFICIENTS (alkali feldspars)
030
92
Tables
Table 1
Table 2
Page 37
Page 38
Page 39
Titles
- - - -- - -- - - - - - - - - - - - - -- -- - - - ------ - - - -- --- -- - - -- -----
95
Page 40
Page 41
Page 42
Titles
-t ..
.. ,.
Tables
Table 1
Table 2
Page 43
Titles
t-='
-
~
....
E
-z:
o
&
(t,0 - tim); AI from T1m to T10
-~---~-
,
,
,
Page 1
Titles
Chapter 4
LATTICE PARAMETERS and DETERMINATIVE METHODS for
H. Kroll
Page 2
Titles
An
BO
60
An [mol%J
40
20
Ab
912
90.0
892
B96
888
894
90B
90.4
880
An
80
60
An[mol%J
40
20
Ab
116.6
1162 f-~----=-i:: --- k: I
Tables
Table 1
Table 2
Table 3
Page 3
Titles
3D
20.
An [mol'!,l
10.
Ab
60.0.
T ['CI
100.0.
120.0.
80.0.
Page 4
Page 5
Titles
91 -
92 -
93 -
94 -
95-
86
87
88
89
90
91
92
93
94
95
c
~?
• No.Co
1\
b
Page 6
Page 7
Titles
4400.'
4Jo.o.'
9600'
950.0'
9900'
98.00·
970.0.'
960.0'
950.0.'
-+-----j 94.0.0.'
Or
25
50
An [mol%]
75
An
Page 8
Titles
ex
>
e
T[l]
Page 9
Titles
100
1000
800
600
T [OC]
400
zoo
o
b (mel)
S2
'1$
-50
a
0(3 (mel)
- (100)
lo
o·
Page 10
Page 11
Titles
t,o-(t,m)
Tables
Table 1
Table 2
Page 12
Tables
Table 1
Page 13
Page 14
Titles
755
760
755
'1, LoY'
1, An JJ - 50
;j? \ + Or - containing
~ ... \ \ /' An 16.5
'i9..
'"
~..r
c High AnO-J3
750 755 no 775
755
780
775
765 770
trll0 [AJ
760
7.70
765
745
750
~760
0'09
10
/ Low Albite
876 Ab 20 40 60 80 An
88.0
90.4
90.8
912
900
6' [0]
896
Page 1
Titles
Chapter 5
OPTICAL PROPERTIES of FELDSPARS
Page 2
Titles
*
Tables
Table 1
Page 3
Page 4
Titles
0.50
o
jt
I ------ __ b ~~
__ 0----1----- no ------ _j
~
~
[ • • •••••••••••••••••••••••••••••• •• ••••••••• • ·1· ••••••••••••• > u
~.: oHIM
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c," :g
I ~O~ KOV oc,V
I A Xf
I o~'I\~«,/ 'rl -Y;{ ~
A'/'''''~ 11'J:f../'A.vOC OF
;7
I
~«, ~;at- I
~,\)'\ ~+~ 7002 I
c:,"",./"; I
.-
REVIEWS In MINERALOGY (Formerly: "Short Course Notes")
Volume
2
SECOND EDITION
FELDSPAR MINERALOGY P. H. Ribbe,
EDITOR
and
SERIES
EDITOR
The Authors Anne
&
M. Hofmeister
George
R. Rossman
Division of Geology and Planetary Science California Institute of Technology Pasadena, California 91125 v Herbert
Kroll
Institut fur Mineralogie Westfaf ische Wilhelrns- Uni versi ta t 4400 Munster, West Germany Paul
H. Ribbe
Department of Geological Sciences Virginia Polytechnic Institute & State University Blacksburg, Virginia 24061 1/
Joseph
V. Smith
Department of Geophysical Sciences University of Chicago Chicago, Illinois 60637 " David
B. Stewart
United
States Geological Survey 959 National Center Reston, Virginia 22092
" Jan Tullis
&,/ Richard
A. Yund
Department of Geological Sciences Brown University Providence, Rhode Island 029 12
MINERALOGICAL
SOCIETY
OF AMERICA
COPYRIGHT Mineralogical
Society of America
First edition Second edition
1975 1983
PRINTED BY BOOKCRAFTERS, Inc. Chelsea, Michigan 48118
REVIEWS in MINERALOGY (Formerly:
"Short Course Notes") ISSN 0275-0279
Volume 2, Second Edition: FELDSPAR MINERALOGY ISBN 0-939950-14-6 -------------------------------------------------------------------------
Aditional copies of this volume as well as those listed below may be obtained at moderate cost fromThe Mineralogical Society of America 2000 Florida Avenue, NW Washington, D.C. 20009 --------------------------------------------------------------------------
Volume 1 SULFIDE MINERALOGY, P.H. Ribbe, editor
(1974) (1975; revised 1983)
284 p. 360 p.
2
FELDSPAR MINERALOGY, P.H. Ribbe, editor
3
OXIDE MINERALS, Douglas Rumble III, editor
4
MINERALOGY and GEOLOGY of NATURAL ZEOLITES, F.A. Mumption, editor (1977)
232 p.
5
ORTHOSILICATES, P.H. Ribbe, editor
450 p.
6
MARINE MINERALS, R.G. Burns, editor
(1976)
(1980; revised 1982) (1979)
380 p. 52~ p.
7
PYROXENES, C.T. Prewitt, editor
8
KINETICS of GEOCHEMICAL PROCESSES, A. C. Lasaga and R.J. Kirkpatrick, editors (1981)
391 p.
AMPHIBOLES and OTHER HYDROUS PYRIBOLES - MINERALOGY, D.R. Veblen, editor (1981)
372 p.
9B
AMPHIBOLES: PETROLOGY and EXPERIMENTAL PHASE RELATIONS, D.R. Veblen and P.H. Ribbe, edLtozs (1982}
390 p .
10
CHARACTERIZATION of METAMORPHISM through MINERAL EQUILIBRIA, J.M. Ferry, editor (1982)
9A
11
CARBONATES,
(1980)
502 p.
R.M. Reeder, editor
(1983) ii
397 p. In press
FELDSPAR MINERALOGY FOREWORD In October
TO THE SECOND EDITION
1975 a Short Course
on Feldspar
Mineralogy
was held at the
Hotel Utah, Salt Lake City, in conjunction
with the annual meetings
Mineralogical
A. Yund, David B. Stewart,
Society
of America.
Richard
V. Smith and Paul H. Ribbe presented powder
diffraction
methods
study of feldspars the nine chapters published titled
and presented
by the Mineralogical
reflect
cluding Volume
optical
techniques
eight lectures,
of which became That book was
the series "Reviews
5 (1st and 2nd editions), written without
of its series en-
in Mineralogy"
of the volumes, this volume
presentation
from the M.S.A.
and a forthcoming
tion, was slowly taking
the present
with resulting
full responsibility
and new contributions
because
shape, no volume on feldspars
Unfortunately
revised
cost
dissatisfaction
Eleven
(see p. ii). Mineralogy
when its
as this, the second edi-
has been available
volume was advertised of patrons.
for this; hopefully
one on
at a short course.
at reasonable
That was a mistake,
to more
some of which __ in-
Three years ago it was decided not to rep rLn t Feldspar second press run sold out.
accepts
to the
Mineralogy.
Society as the second volume
renamed
are now available
were accepted,
and
as applied
the substance
of Feldspar
the scope and contents
fluid inclusions --were
two years.
Joseph
on x-ray single-crystal
Notes".
In 1980 the M.S.A.
volumes
and electron
of the first edition
"Short Course
accurately
workshops
of the
for
and orders
The series editor
the updating,
in this edition will in part compensate
improvements, for the incon-
venience.
It will be noted by readers new ideas appearing by review research greater
in Chapters
(other than ourselves) community.
Inevitably,
topics, some repetition
structures
and diffraction
libria and exsolution editor has attempted throughout
emphases.
the volume
received
of material
scrutiny
tests of time in the decided
the
soon to be outdated.
goals of individual
authors
has occurred,
in their
although
and their Al,Si distributions,
are featured,
to cross-reference as feasible.
books of this series produced with the detailed
practical
usually
Chapters· 1, 2, 9 and 10, in which plagioclase
patterns
textures
that there are many
in this, but the editor
a review volume
given the different
with quite different
with feldspars
nor survived
There is some danger
risk was to produce
assigned
experienced
3, 4 and 5 that have neither
are notable
This is a luxury not afforded
compensates
in other
and it, together
to some degree for the lack
of an index. Paul H. Ribbe Series Editor Blacksburg, VA April 30, 1983 iii
The
these and as many other subjects
with a short course deadline,
Table of Contents,
phase equi-
in this regard.
ACKNOWLEDGMENTS Throughout these
by Joseph debted many
this book
are Volumes V. Smith
to Drs. figures
following
repeated
and published
Konrad
We also for of
(and hopefully
discussions
pitch,
of which
none
scientific authors
progress.
are
in advance
lent
great
and Ada
of Geological
University
are
viding
thanked
rewriting, facilities
text
at the M.S.A.
edition
of Feldspar
Carnegie
of the
figures:
benefitted
of which
and criticized
many
are
patience
and
Mineralogy,
with
The
for data
for perseverance
and her
him
during
of the
and
State
the long process
of the University
abuse
two years
for excel-
staff
Institute
acknowledged,
much
staff
the secretarial
Support
suffered nearly
for figures,
Polytechnic
is gratefully
a high
some palpable
and correction.
Chiang
at Virginia
who
produced
to be commended
Sharon
from numerous reached
of the chapters.
scientists
and composing.
office
greatly
some of which
and several
colleagues
for their
Institution
Longmans Springer-Verlag
and
Sciences
(and salary!)
friends
and publishers
Journal of Geology Philosophical Magazine Proceedings of the Japan Academy Petrographische Mitteilungen Manchester University Press
Simmons
the
editing
in-
to reproduce
to reprint
for encouragement
The editor's
Department
the editors
individual
and
in typing
draftsmanship.
writing,
read
to numerous
Strickler skill
for permission
B. Stewart,
to blows,
of publication,
Margie and
David
Stewart
grateful
written
We are particularly
permission
this volume)
with
came
(1974a,b); work
Science The American Mineralogist francaise d~ Hineraiogie et de Cristallographie Contributions to Mineralogy and Petrology
re c e
The Feldspars Geochemical Transport and Kinetics Rock-Forming Minerals Electron Microscopy in Mineralogy
The editor
thank
their
Geochimica et Cosmochimica Acta Mineralogical Journal, Japan Physics and Chemistry of Minerals Schweizerische Mineralogische und
stimulating
to Smith
an encyclopedic
and H. Wiebking
and books
The American Journal Bulletin de La soc Chemical Geology
are made
Minepals,
by Springer-Verlag.
Springer
free of charge.
journals
references
2 of Feldspap
1 and
of
in pro-
as are his A.G.D.
over
back-orders
for this
overdue.
SELECTED REFERENCE WORKS The following lished
in
is
a list
recent
of
Feldspar
Minerals,
1.
Crystal
Feldspar
Minerals,
2.
Chemical
Verlag: The
works
New York.
627
Structure and
and
690
Solutions Solides en Min~ralogie, Edited by G. Saba tier (1974). Microscopy
Berlin. Thema
on feldspar
mineralogy
pub-
and
Physical
Textural
Properties,
Properties.
By Joseph
V.
Smith
(1974),
Springer-
pp. Institute, Manchester
Manchester, University
England. 1972. Press: Manchester.
pp.
Electron
525
in
Soc.
Edited
International
franc. by H.-R.
du C.N.R.S.
Min~raZ.
cri.etial.loqv-
Wenk and
G.
Thomas
No. 234, Orleans, 97,89-404. (1976).
1974.
Springer-Verlag:
Sohuei zeri-eche
Mineralogische
und Petrographische
Mitteilungen
47/1,
pp •
Rock-Forming
Minerals,
Longmans: Proceedings Christie
London. of
the
Framework 1-178.
317 of Edited
Silicates.
Study
Norsk Geologisk
--Phase Relations. Translated from
Jerusalem. Proceedings
4. pp.
NATO Advanced
(1962).
Feldspars Marfunin.
1983.
Co Ll.oque
euu:
Mineralogy.
pp.
Pe Ld sp a t e , 1967.
398
The
reference
Feldspars, Proceedings of a NATO Advanced Study Edited by W. S. MacKenzie and J. zus sman (1974),
717 Les
useful
years:
the
By W. A.
Institute
Tidssk:rift
Optical 1962
Deer,
of
Feldspars,
42/2,
606
R.
Olso,
A.
Howie,
1962.
and
Edited
J.
Zussman.
by
O.H.J.
pp.
Properties, and Geological Distribution. Russian edition, 1966. Israel Pr og . Sci.
By A. S. Translations:
pp ,
a NATO Advanced by W. L. Brown,
Study
Institute
untitled
at
on press
iv
Feldspars time.
and
Feldspathoids,
Rennes,
France.
FELDSPAR MINERALOGY TABLE of CONTENTS Page COPYRIGHT; LIST OF PUBLICATIONS
ii
FOREWORD TO THE SECOND EDITION ACKNOWLEDGMENTS;
CHAPTER
iii
SELECTED REFERENCE WORKS
iv
1.
The CHEMISTRY,
STRUCTURE
and NOMENCLATURE
P.H. RIBBE of FELDSPARS
INTRODUCTION
1
TOPOLOGY OF THE FELDSPAR TETRAHEDRAL FRAMEWORK
2
The a-axis projection
3
The e*-axis projection
6
The b-axis projection
6
Idealized cell parameters
9
PATTERNS OF ALUMINUM, SILICON ORDER-DISORDER: NOMENCLATURE BASED ON STRUCTURE AND CHEMISTRY Alkali
(Na,K) feldspars with Al:Si
Ca- and Ba-feldspars with Al:Si
=
=
9
1:3 and e ~ 7 K
2:2 and e ~ 14
9
K
12
I2/c eelsian pi anorthite Ii anorthi te
14 14 16
Summary of feldspar site nomenclature Antiphase domains and the
CHAPTER
Ii
17
average structure
2.
19
P.H. RIBBE ALUMINUM-SILICON ORDER in FELDSPARS: DOMAIN TEXTURES and DIFFRACTION PATTERNS
INTRODUCTION SEQUENCES OF Al,Si ORDER IN ALKALI FELDSPARS Ordering in K-feldspars
. . . . . . . . . . . ..
involving a monoclinic+triclinic
inversion
Development of polysynthetie tioinein mieroeline Untlilinnedor simple-tlilinnedmieroeline One-step or tiao-etiepordering? Temperature seale for the sanidine+mieroeline inversion Ordering in triclinic alkali feldspars Potassium feldspar Sodium feldspar
21 22 22 24 28 28 30 30 30 30
Page
CHAPTER
2, continued
SINGLE-CRYSTAL DIFFRACTION PATTERNS OF PLAGIOCLASES • . . • • . . . •. X-ray techniques
31 32
The preeession method The oseillation method
32 32 33
Summary of plagioclase diffraction patterns
39
SEQUENCES OF Al,Si ORDERING IN PLAGIOCLASES
40
Ordering in sodic plagioclases
40
Albite Peristerites
41
Average structure models of plagioclase
42
Ordering in calcic plagioclases
44
44 48 48
Anorthite Bytownite High plagioelases Huttenloeher intergrowths
49
Ordering in plagioclases of intermediate composition
50
'e '-plagioelase B~ggild intergrowths
51 54 54
SUMMARY .
CHAPTER LATTICE
50
o l iqocl.aee
3. PARAMETERS,
H. KROLL & P.H. RIBBE COMPOSITION
and Al,Si ORDER in ALKALI FELDSPARS
INTRODUCTION
57
TETRAHEDRAL SIZE AND Al,Si DISTRIBUTION
58
A linear model
58
A new model
67
Correction of bonding effects
69
LATTICE PARAMETERS OF ALKALI FELDSPARS
70
Alkali exchange series
70
Cell volume and the a dimension
74
The band
75
e cell dimensions
THE b-e PLOTS TO DERIVE (tlo + tIm)
77
THE a*-y* PLOT TO DERIVE (tlo - tIm)
79
STRAINED FELDSPARS
81
• • . • . . • • •
THE [1101 METHOD FOR DETERMINING Al,Si DISTRIBUTIONS
84 85
Basis of the [110] method The [110] method for alkali feldspars
87
Diagrams to estimate tlo and (tlo - tIm)
89
vi
CHAPTER
3, continued Page
ESTIMATION OF ERRORS OTHER DETERMINATIVE
93 METHODS
94
PETROLOGIC APPLICATIONS
96
Ordering paths
96
Suggested convention for plotting Al,Si distribution data
98
CHAPTER
4.
H. KROLL LATTICE PARAMETERS and DETERMINATIVE METHODS for PLAGIOCLASE and TERNARY FELDSPARS
INTRODUCTION
101
LATTICE PARAMETER VARIATION
103
High plagioclases
103
Low plagioclases
106
Thermal expansion
107
THE [110] METHOD FOR PLAGIOCLASE FELDSPARS
•••••••••
e .••
110
Diagrams to estimate tlo and (tlo - 1 µm) to be seen in thin section (where it is sometimes mistaken for fine scale twinning). An electron diffraction pattern of an exsolved specimen of bulk composition An72_75 (Fig. 12) was discussed in the previous section. It is remarkable in that it shows nearly every type of diffraction phenomenon known to occur in the entire plagioclase feldspar series.
The sharp 'a' and 'b' and diffuse 'c'
and 'd' reflections arise from the transitional anorthite (An~90)' which undoubtedly has hundred Xngstrom scale 'c'-domains and coarser 'b' domains (see table above). The average structure of the more sodic phase, an 'e'-plagioclase of composition An~65' has lattice parameters very close to those of An~90' thus its 'a' reflections superpose on those from the calcic phase.
The antiphase super-
structure which produces 'e' and 'f' reflections is imaged in Figure l3b; in this particular specimen the periodicity ranges between ~32 and ~37
X
due to
compositional inhomogeneity, which may represent a secondary stage of exsolution. In general, the two exsolved phases coexist as complicated lamellar intergrowths on the scale of a few hundred Xngstroms to optically visible (micronscale).
The's'
streaks through the 'a' reflections (Fig. l2) are inclined to
b* and c* and are approximately normal to (031); they result from the imperfectly developed (031) quasi-periodic lamellar "superstructure" of alternating slabs of calcic and 'e'-plagioclase, like those illustrated in Figure l4-l6 in Chapter lO.
A second lamellar set parallel to (301) is sometimes observed.
X-ray patterns never give clues to the orientation of exsolution lamellae, but if the average total thickness of an An~65 1350 to 2400
X,
+ An~95 pair is in the range of
interference colors may be visible from a plane which is paral-
lel to their interface (see Ch. lO, pp. 266-270).
49
Ordering in plagioclases of intermediate composition First we will discuss the structures of two low plagioclases which showed only 'a' reflections in x-ray photographs. Oligoclase.
Average structures of two oligoclases, Anl6 and An , were 28 reported by Phillips et al., (l971). It is assumed from their pegmatitic occurrences that they are as ordered with respect to Al and Si as is possible, and indeed their diffraction patterns, lattice parameters (Chapter 4) and optical properties (Chapter 5) indicate structural states consistent with low-temperature equilibration.
However, their Al,Si distributions are far from ordered
in either the low albite or
pI
anorthite sense.
Data are shown in Figure l6
and recorded in Table 1, Chapter 3. Because T10 is Al-rich and the other three T sites are equally Si-rich, it is clear that, just as in albite, Al concentrated in TlO as these feldspars inverted from their respective disordered arrangements.
But tlo is signifi-
cantly less than l.O in both An16 and An28, even though there are l.16 and l.28 Al atoms available in these structures to fill TlO. This is one limiting model for low plagioclase -- we will call it "full T 10".
Another possible model in-
volves mechanical mixtures of the two fully ordered end members of the plagioclase series, low albite [LA; tlo =1.0, =~(tlm+t20+t2m)
= 0.0) and anor-
thite [An; tlo =tlm=t2o =t2m=0.5; Eqn. 2 above). The Al distributions expected from these are listed below in contrast with the "actual" values determined from crystal structure analyses using Equation 5, Chapter 3. nAn = 0.16
Model tlo "full tlo" mech'l mix "actual"
1.00 0.92 0.815
nAn = 0.28
tlo
0.053 0.08 0.115
1.00 0.86 0.68
--_---
0.093 0.14 0.20
Clearly there must be an ordered LA structurql "component" to account for the concentration of Al in TlO, and an anorthite structural "component" to account for the observed composition, and, in order to raise the Al content of Tlm, T20, T2m to the "actual" tlm, t2o, t2m values; one might add a third "component" that consists of disordered albite (call it analbite, AA) which in turn must be subtracted from the LA "component" to keep the formula balanced.
If
the fraction of anorthite "component" in such a model is given as nAn' then the fraction of AA is 4[obs - ~An) and the fraction of LA is [1 + nAn - 4obs). For low Anl6 and An28 the values are l6:l4:70 and 28:24:48, respectively. To explain the observed Al,Si distribution of these and other low 50
plagioclases, Smith and Ribbe (1969) proposed a model similar to this but which involves coherent out-of-step domains, on the scale of ten or more Xngstroms, consisting of alternating ordered LA-like and An-like structure in a continuous tetrahedral framework.
Between the two types of ordered structure are bounda-
ries in which some degree of Al,Si disorder must exist because of the topologic incompatibility of the 1:3 and 2:2 ordering patterns. tributions in the four T sites of the Cl, 7
X
The reported Al,Si dis-
cell represent an average of
that which exists in these domains and the disordered boundary regions separating them.
This model is discussed in more detail below.
'e '-
.... ....
•
0 E NO
•
o
N
k
+)
+ E
t..
(I...
",,"""'C +l
E
Q) ..
o
.-t
II
Q)
.: ~ '" Q)
.c .... ...
...o '"
Q) U
c: co
~"
....
" co
Q)
.... U 0
o
'"
c:
~
.... CD
a. '"Q)
'tJ III
'"
U
'tJ
co a.
.... co
:J U U
co
'c:
>. ....
c
0000
....
~
~
c:
>-
....
:::J
m
o
0
c: co
...
......
....:J
0000
N
Q) U
o
rl
..
IJ)Lt1Ln ..-00'\ ..-NN
-o
o
'"
'"
c:..c.
>-
"
C 0
m
.
V
Lt1UiU1L{} nn..;:to NNNN
E ~ 0.:
Q)
.,µ ·rot
m
1:J x..µ
t"-t"-t"-t"-
00lf)Lt1 0000 0000
tn
....c: ...co
Q) E
rn
'"
o
-..-I
u
ro
c:
s:
0
oot")t")nLDU1Lt1LnO\ "-L[)lf)lJ1U1U1U1U1lf) 1.0\.0\0\01.01.0\0\01.0
o
........
'.-4
+)
Q)
V 'tJ
(l • ....
.......
+)
m
rllM ~
l-.....
•
...
co a.
"'C
tU
s:
U)
U U
m .... ..... "'C
m
s:
'"
k
E E Q) N N.c
.L:..c.c:J
1:J ..µ
'"
....
Q)
..j..J
m
r-4
1:J ..µ
'"
en
.>.>.>. [IlCO[DCO
.......... .r:.r:.r: .......... ... ... Q)
Q)
Q)
•..-l ...... ..-l
...
000
c: c: c: cc e; < mlno N
N
t"J
'"
'"
_0\
_en
U")q
U")q
qO \0 U") \O~
.0'" o>r-
0.:
~
~I
';,', "'-
1
ttl'
: I "I 0
co ..... 000'\
co com
r-- ..... rom
",roen
00 00
t"1C'0'\ 0
"' en
00
en en
en en
N~
r-O
r-O
r-O
co CD en
"'''' NO
o>~ N co
CD ",en CDN
lll
in
o ~o> CD
tn
N
N
OlN 1'1r",r-
NO
"'N Ol~
coo
'"
co
r-N Ol~ U'l~
'"
o eno Ol'" U'l~
NU'l N~
CD co co en r-N Ol e-
'"
en "'en Ol e-
Ol ~O ~O ~
a> .µ
"
c
c
~I"
rl
a> u,
E a>
....
c:
o
a> .µ
c: N
c
E
c
E
N U
'" u
a.
E
'tJ
N
a. c
" '"
'"
o
u r-
U'l 1'1
....E"
...."
E
...."
E
..,"
E
E
E
E
E
...."
E
E
...."
...."
...."
...."
a>
a>
c:
c
U'l
a>
c
a>
c
co
66
a.
""
'" ....c"
...."
E
c
::J
N
E :3
o
..J
...."u
E :3
o -'
for anorthite, 1.613 and 1. 742
A
for low albite (Table 1;
average of four refinements), and 1.613 and 1.738
A
for low microcline
«AI-O»
= 1.747
A
(Table
3 and Blasi et al., 1983; average of five refinements). The «T-O»
versus diagram (Fig. I) covers the range from 0.25 to 0.5
Al/(Al+Si), and even if the bonding effects just mentioned were insignificant, long extrapolations from 0.25 to 0 and 0.5 to 1.0 would be necessary to represent the full range of t values in individual tetrahedra.
This leads to sys-
tematic discrepancies, and Smith (1974a, p. 70) "in desperation" suggested using two separate straight lines in the regions of 0 to 0.5 and 0.5 to 1.0 Al/(Al+Si), but with limited success.
Direct refinements of site occupancies
by neutron diffraction methods are few in number and not without their own difficulties (see footnote 1). A new model Ribbe (1975, p. R-22) suggested deriving Al contents of T sites, not from the distances themselves, but from differences in mean distances.
His
method eliminated some uncertainties of the linear models that arose from long extrapolations and from the fact that the mean AI-O and Si-O distances are different in the different ordered structures, namely but did not account for bonding effects.
LA, LM and
pi
anorthite,
Furthermore, it did not permit an
independent determination of Lt apart from a knowledge of nAn (see Eqn. 3). This last problem may be overcome by considering the differences between average individual and grand mean tetrahedral distances, i.e., «T-O»,
rather than size differences among individual tetrahedra as in
Ribbe's model.
The procedure for calculating site occupancies may be recast
into a single equation if we consider separately the difference 6t between the individual and the average values of t: 6t
=
t. -
or
1.
ti
=
+ 6t .
(4)
is found from chemical composition by Equation 1, and 6t is related to - «T-O»,
so that Equation 4 becomes ti
where 'const'
=
=
«Al-O»
0.25(1 + nAn) + «Ti-O> - «Si-O»;
spars and is taken to be 0.13
A
- «T-O»)/const
it is equal to 0.125
X
,
(5)
for K-rich feld-
for Na-rich feldspars and plagioclases.
At this stage, the An-content still must be known in order to find ti. Figure
However, we can-eliminate this by expressing in terms of «T-O».
1 indicates that the linear model must be modified for this purpose by (1) treating the An-rich plagioclases separately, and (2) considering that the
67
«T-O»
distances of ordered feldspars --especially
alkali feldspars and souic
plagioclases -- are slightly larger than those of their disordered equivalents. Since it is desirable to substitute by «T-O»
in Equation 5, we chose
as the dependent variable in a regression analysis of the data listed in Tables 1, 2 and 3 (excluding An-rich plagioclases): = 0.25(1 + nAn) (6)
-11.215 + 6. 981 «'['-0» + 0 .124 «T I0-0> - (±.076) (±.017) I with a correlation coefficient given in parentheses. order present.
r2 = 0.996.
Estimated standard deviations are
The third term on the right accounts for the amount of
When TIO and Tlm tetrahedra are identical in size, Equation 6
reduces to the original linear model.
The values of expected from chemical
composition are reproduced with a standard deviation of +0.005 Al/(AI+Si), responding to
±
cor-
2 mol % An.
An analogous equation for An-rich plagioclases
The reason why «T-O»
=
is (7)
-12.088 + 7.491 «T-O»
distances of An-rich plagioclases
be expected from sodic and intermediate
compositions
are larger than would
is open to question.
One
is tempted to ascribe it to some bonding effect due to Ca, but the substantial discontinuity fined in
II
pi
near An in Figure 1 is disturbing, as is the fact that An98 re80 by Bruno et al. (1976) gave «T-O» = 1.681 A, but refinement in
gave 1.678
A.
Combination occupancies sition.
of Equation 6 or 7 with Equation 5 allows uS to derive site
from distances without making reference to chemical compo-
This procedure is indicated when the total Al content so derived is
to be checked against the Al content expected from the chemical formula: should not differ by more than 2 mol % An.
To simplify calculations,
they
it is
safe to assume that tIm = t plagioclases microclines
(Table 1; cf. (Table 2; cf.
0 = t m for all natural Na-rich feldspars and 2 2 Fig. 16, Ch. 2) and t20 = t2m for intermediate
Fig. I, Ch. 2).
A sample calculation
for inter-
mediate microcline AID (#5, Table 3) follows.
for T 0 = 1.673, TIm 1
= 1.651, T20 = 1.623, T2m - 1.622
0 = 0.25 + (1.673 1 tIm = 0.25 + (1.651
t
and
t
2
0
1.642)/0.125 = 0.50 1.642)/0.125 = 0.32
= t2m = 0.25 + 0.6225 -l.642)/0.125
68
A;
= 0.09
«T-O»
l.642 A
Correction of bonding effects As mentioned
earlier, a statistical
study of bond length variation in
feldspars by Phillips and Ribbe (1973a) and Ribbe et al.
(1974) produced three
factors, in addition to Al content, which perturb individual T-O bond lengths:
A
(I)
Linkage
Si-O ~ Si bonds are ~0.03 Si-O -+ Al bonds.
(2)
Bonds to Na,K,Ca
The coordination number (2, 3 or 4 in feldspars) of the oxygen atom is related directly to T-O distance.
(3) T-O-T angle
longer than
Longer T-O distances are associated with narrower T-O-T angles.
Strob (1983) has completed an elegant study of alkali feldspars in which he has produced regression equations to correct for these effects. to observed distances reach !0.005 standard deviation in .
Adjustments
about three times the estimated
Their importance is that they adjust for what are
small, but obviously systematic, individual tetrahedra.
A,
errors in our estimation of Al contents of
They have less importance in our subsequent discussion
of the derivation of ti values from lattice parameters
than they do for model-
ling the precise details of Al,Si ordering paths, for example, that are shown in Figure 8bin Chapter 2 for Na-feldspar.
The effect of these is to slightly
decrease the value of and increase
and thereby redistribute
estimated Al contents, for which Strob has derived a somewhat modified version of Equation 5. K-feldspars
Two examples suffice to illustrate the results for Na-feldspars;
are generally much less affected. Observed ~_m~
Tiburon HA #'; in Toble I
Site
F99 »F91.
c To
determine aestimated from b·c, use the following regression equation: 1
aest = 8.634 - (11.437 - 0.12226 b'c)1
6a
=
aobs - aest' as defined by Stewart and Wright. Stewart
(1975) comments, "The effects of certain components sometimes
and H 0+?) may be confused with the 3 effects of coherence, so that if a feldspar is known to be homogeneous and a found in alkali feldspars
(B, Fe, NH:,
significant 6a is observed, composition should be carefully checked. volume of a strained feldspar is only a first approximation
The cell
to the cell volume
BThe plane of intergrowth is close to (100). Thus in the potassic phase band C will be smaller than "normal," a will be larger, and vice versa in the sodic phase.
R2
MONOCLINIC
TR1CLINIC
692 A3) with various values tlo. The equation to start with was that for K-rich low alkali feldspars (Table 5), the slope and intercept of which was changed with tlo such that the straight line representing tlo =0.38 was parallel to the Nasanidine line.
Thus, the equation for the contours takes the form:
tr[lIOj Thus
tr[lIOj
IlTriclinic adularias, grown within the micro cline stability field, may deviate from this line. The equilibrium tl value of the sanidine + microcline inversion, which cannot be directly observed, can at least be approximated: sanidine from Volkesfeld, Eifel, has tl = 0.315, according to four structure refinements (Table 2); 'Spencer C' orthoclase has tl = 0.36. The equilibrium value can thus be assumed to be tl = 0.34±0.02.
89
Table 5. Variation of tr[lIO] and tr[lIO] - tr[110] with cell volume V in the limiting series analbite-high sanidine (AA-HS) and low albitelow microcl1ne (LA-LM) (Figs. 10 and 11): tr[lIO]
a
=
1
+ a2V and tr[110]
LA-LM series:
tr[lIO]
- b1
2
a
Coefficients
AA-HS series:
-
2
b
a '10 2
1
+ b2V. 1
b '10 2
V
< 692 R3
5.6103
0.30373
-.8393
0.12128
V
> 692 R3
5.4396
0.32747
0
0
V
< 692 R3
5.5129
0.28978
-.3813
0.09933
V
> 692 R3
5.0123
0.36213
0.6452
-.04902
I
780 776l
t10
..Al = 1.0. Data for a Lb t t e s from Hartin (1970, Table 1) are shown by circles, most of which f n Ll on the one-e tcp ordering path, and triangles, which do not. Nafeldspar snmo l c s 393, 1219 and 1216 (formed at 200-250°C) apparently have AI-enriched 7' m sites. It is po s s t bl e t hc se samp Lc s partially ordered meta stably with monoclinic symmetry befo~e becoming t r t c l Ln t c (see Ch . 2, Fig. 8). In t e rmcdin r o mi croc lines (solid Jots) studied by Guidotti, Herd, and Tuttle (1973) order along a path where ,\1 moves to TIO from TIm approximately q times [aster than f rom T 0 and 1'2m 2 c omb i n cd . The shaded area with 0 -= tIm d La cr amms t Lc a Ll y represents the relative abundance of l the monoc l i n n- feldspars [rom the s.3me region. Monoclinic feldspars from th-is area ordered further with mnl1~t;.H·
c,"
~c:,;
Or
~ /~~~~
0.20
Triclinic
I
I I I
I
0.30
(}W
a
0.40
uncertain
(1979 I ... Spencer
(1937)
Wondrotschek
O.A. P. II (010 I
O.A.P.(-I.L(OtO) O.A. P. .L (010)
(1981)
? Symmetry
A, B,C(htdl
Y1\f DePieri
)( 'J:f.. Preiss
Monoclinic
+ Zeipert
•
t;.
I
OF
o Monoclinic
;7
11'J:f../'A.vOC
"'I\~
l>u
(1981)
ye
t;.
'!f
----.--
~
t;.P 0
.
0,50
0y.o~
~«,
oc,V
7007
oB °z
~,c,~
KOV
:g
~.: oHIM
O.A.P.(-).L(OIO)------~---
I
I I
0.0
/,W-I
7002
:
I
I
'/'''''~
A
(010)
~«, ~;at~,\)'\~+~
;)
c:,"",./";
.-10-12cm2sec-l).
are simultaneously
is com-
to determine
et al., 1978).
a hole
the
One of the principal
if
(e.g., Giletti
and by assuming
technique
in order
and it gives large
near
can be determined. years,
feldspar
temperature,
A sectioning
annealing.
resolution,
is used to sputter
is subsequently tration
after
(>10-18cm2sec-l)
mined with an ion microprobe
can be implanted
thickness,
is relatively
can be determined
in the ion probe
1977).
a layer of known
tions of this method the diffusion
which
or the isotope
direction enables
method using
is to determine
the ion microprobe
the diffusional
as providing
a completely
anisotropy different
coefficients. 206
the isotopic
profile
(e.g., Giletti
in the crystal method
in a specific
et al., 1978).
This
to be determined,
for determining
diffusion
An important question with regard to the hydrothermal technique concerns how the isotopic exchange occurs.
In the original study (Merigoux, 1968), it
was assumed that only lattice diffusion contributed to the isotopic exchange unless the grains and fluid were out of chemical equilibrium.
When the Na/K
ratio of the feldspar and the fluid is far from equilibrium, the grains are reconstituted by a fine-scale dissolution and reprecipitation process (O'Neill and Taylor, 1967).
At high temperature, and probably at high pressure where
solubility is greater, the grains may be modified by dissolution and reprecipitation even if they are in chemical equilibrium with the fluid.
The amount
of dissolution and reprecipitation is temperature-pressure-time dependent, and the window for lattice diffusion measurements of ions in any mineral must be determined.
Untwinned and disordered overgrowths on grains of a maximum
micro cline were used to demonstrate that only lattice diffusion contributes to the isotopic exchange below about 800°C and 2 kbar water pressure (Lin and Yund, 1972). Additional proof that the rate of isotopic exchange between feldspar and fluid is controlled by lattice diffusion is provided by the different isotopic exchange rates for potassium and oxygen in the same feldspar at the same temperature and pressure (Yund and Anderson, 1974).
A difference in the rates
would not be observed if the exchange was due to a mechanism other than lattice diffusion.
Finally, there is very good agreement between the results
determined by the integrative and ion microprobe methods for potassium diffusion in low albite (Kasper, 1975; Giletti et al., 1974), and for oxygen diffusion in adularia (Yund and Anderson, 1974; Giletti et al., 1978).
If dissolu-
tion and reprecipitation significantly contributed to the exchange, the results from the two methods would not agree and the isotopic gradient would not be a diffusion profile. Inter-diffusion coefficients are commonly determined by bicrystal experiments in which two crystals of different compositions are polished and held together during the anneal (e.g., Christoffersen et al., 1981). concentration profile is measured with the electron probe.
The resulting
Diffusion aniso-
tropy can be determined by this method, and the principal limitation is that it is difficult to accurately determine D values less than about 10-14 cm2 -1
sec
_
[An ion microprobe could be used to determine smaller D values.]
Petrovic (1972) used a variation of this technique which involved the partial exchange of alkalis between a crystal and molten chloride. A recent technique for determining an average interdiffusion coefficient for a compositional interval is based on the rate of homogenization of 207
exsolution 1980;
lamellae
Brady
Electrical these
data
fusion ment
conductivity
of multiple
boundary
profiles
is used
is known. width,
charge
carriers
(Brady
to limit
across
to extract
the grain
The quantity
determined
and McCallister,
diffusion
in silicates, (Maury,
boundary
of this method.
the determination
of dif-
and a mathematical
diffusion
coefficient
Dgb times
boundary
coefficient
width
The
of which
boundary,
is actually
and
1968).
identification
the usefulness involve
a grain
of the grain
transport
coefficients
and the actual
measurements
in a sample
an effective
to ionic
diffusion
appear
diffusion
and the evaluation
Commonly,
and thickness
is related
is (are) functional
Grain
composition
in press).
can be used to estimate
possibility one(s)
of known
and Yund,
Dgb when
the grain
is rather
is used which
treatD
t
boundary
subjective.
is the product
of
Dgb and the width.
EXPERIMENTAL The feldspar were
perthitic
1952;
samples
Sippel,
1963).
for volume
sonably
good agreement
composite
ferent
diffusion. with
measurement studies
types
considered
not
any further
In the following
as identification
particular
diffusion
of the topics figures
provide
interval
was
ficient
normal
others
are in rea-
are clearly
diffusion.
and the effect
These
studies
Jensen,
of these
1963)
in detail,
meaningful
questions should
a
The samples
studies
only
results
evaluation
and problems.
be consulted
were
will
of the difnot be
in the text where
are arranged
by
of the data as well Some of the data are
for information
determined.
comparison
the data were
However,
about
the data
how
for some
they are discussed.
The
of the data and show the temperature
determined.
in feldspar
of sodium
diffusion
by Bailey
to (010) was
to (001), but within
(Sippel,
and volume
the experimental
coefficients
investigated
1949;
the validity
whereas
be evaluated.
a more
and these
of diffusion
data,
diffusion
here. discussion
a convenient
The anisotropy phere
recent
cation
(Rosenquist,
to evaluate
boundary
cannot
are presented
over which
Anisotropy
more
of remaining
in tables,
crystals
characterized
this permits
presented
of the earlier
Some of the results
of grain
were
of diffusion
topic because
in most
not single
It is difficult
studies
in these
used
or otherwise
RESULTS
in an albite
(1971).
He observed
0.1 to 0.6 as large
his experimental
error 208
at 595°C
and one atmos-
that the diffusion
as that for diffusion
these
diffusivities
coef-
normal
could be equal.
Petrovic normal
(1972) observed
to (010) than normal
fractures
and spallation
diffusion
rates
diffusion
normal
data,
normal
of that normal
to (001) and
in low albite
to (010) was one tenth
at 1000°C
that normal
and 15 kbars
to (010) is one tenth
alkali
parallel
we will
diffusion
half
expect
the diffusion
800°C
and 1-2 kbar
to (001), (spherical) Effect
(010),
(Ill), and
The early
hydrostatic
diffusion
parallel pers.
as the simplest
by
and normal
to [011]
comm.)
to that parallel
coefficient
normal
indicate to [011].
approximation
for
would
equal,
be the same
has been
et al., 1978).
1977)
The anisotropy
but
for these
The diffusion
is
of
it is reasonable
investigated
(130) are approximately
indicate
to (010) in a micro cline
to (001) in an orthoclase.
diffusion
pressure
studies
pressure pressure
of alkali
within
and the pressure at 1000°C
diffusion
coefficient
diffusion
experimental
range was
normal
that the activation
on alkali were
None of these
small.
(Christoffersen
3), and that the effect can be disregarded
and water
of 1-2 kbar.
diffusion
appears
results
adularia
interdiffusion
(Christoffersen, equal
by the normal
to
ions.
in two albites
coefficients
consistent
with
at
normal
an isotropic
model.
of hydrostatic
or a water
stant
(Giletti
of
sections.
anisotropy
of oxygen
between
that alkali
model
determined
Preliminary
interdiffusion
need not be numerically
that the relative
one hundredth
coefficient
(Misra and Venkatasubramanian,
of that normal
The anisotropy
but
The details
profiles
to (001) at 800°C.
use a cylindrical
diffusion
equal,
to unpublished
about
1974).
the diffusion
to [100] is about
in the following
that at 800-870°C
Sr and alkali
that
results
The data for Sr diffusion
only about
to
the alkali
about
In reference
to (001), with
Preliminary
that interdiffusion
that
were
(Petrovic,
also indicate
that normal
intermediate.
difference
to (010) was
that potassium
indicate
et al. (1981) for alkali
Christoffersen
Nevertheless,
slower.
is slower
published.
et al., (1974) reported
Giletti ion microprobe
being
(110) of adularia
somewhat
not been
this
He also reported
to (110) at 890° and 1000°C have
in an albite
to (001), but he ascribed
that Ln t.er dif f us Lo n normal
experiments
albite
interdiffusion
of the crystal.
to (120) was
he reported
these
that alkali
either studies
done
at one atmosphere
observed
error,
but other
A more
recent
any effect
factors
study
were
of alkali
et al., 1981) found no difference
to (001) between volume
diffusion
for alkali
of hydrostatic
pressure
in most mineralogical
209
of
not coninterin the
five and 15 kbar.
Thus,
diffusion
(see equation
is small
on alkali
applications.
diffusion
it
in feldspar
The effect
of water
is somewhat
coefficients
determined
1972)
appear
to be consistent
other
factors
are taken
into account.
tion lamellae
in alkali
feldspar
samples
are annealed
1978).
Goldsmith
attainment alkali
answered.
section).
confining
pressure
have been
800°C
for several
before
dicating
that the trace
of water
diffusion
1 and plotted
data.
The high-temperature and albite
chlorides.
These
Data agreement
800°C
for high
salt experiments
was vacuum
when
the
experidried
(Christoffersen, for an undried
for Na and K, which
1, show
good agreement
disagreement
data were were
have
at
pers. sample,
sample
in-
did not
temperature
those
a lower
in some respects
Na diffusion
K diffusion
for adularia
in orthoclase
210
assumptions
profiles
alkali of magnitude) of ideality
(curve
8) are in fair
shown by curve (curve
as given
energies
diffusion
molten
on composition.
in adularia
in orthoclase
the activation
with
and include
and poor
temperature
(up to an order
coefficient
in
some of the high
from alkali
exchanged
precision
data,
for Na diffusion
However,
are summarized
is between
calculated
partially
temperature
that for K diffusion
interval.
diffusion,
interdiffusion
which
the
(see later
is only effective
wt %) in the undried
of the self-diffusion
ly, the high-temperature ment with
the molten
Alkali
those
affects
oxygen
2, 4 and 8 in Fig. 1) and the lower
which
results
of the lower
with
that
in
completely
temperatures
the Pt tube
(~.02
diffusion
greatly
enhances
of water
a bicrystal
coefficients
(curves
in adularia
than most
on the
rate may not be
on alkali
to lower
kilobars.
agree with
The greatest
results
and independence
the
at 15 kbar.
on Figure
in others.
temperature
the
coefficients
The self-diffusion
agreement
enhances
experiments
of water
greatly
creep
sealing
results
Table
feldspar,
several
The preliminary
diffusion
greatly
not be considered
amount
or that a trace
is above
hours
of water
probably
must be considered
comm.).
Alkali
that water
in reversal
done at 15 kbar with
the alkali
when
exsolu-
(Yund and Davidson,
this reaction
of dislocation
of water,
affect
pressure
to be the same whether
pressure
although
that even a trace
The possibility
ments
Lin and Yund,
of coherent
at 10 kbar
should
rate of alkali
the field
traces
appears
lack of effect
the question
contained
1974;
The rate of growth
report
solvus,
of the apparent
disordering
1972,
diffusion
diffusion.
It is known
and extends
Alkali
done at 1-2 kbar water
at S60°C
equilibrium
by lattice
In spite
(Petrovic,
those
(1974)
strain-free
most experiments,
problematical.
in air or at 2 kbar water
of chemical
controlled
salt
with
and Newton
feldspar
Al/Si
in molten
more
9.
Similar-
2) is in fair agree-
by curve
for these
3 in the 600-
two sets of data
·16-1 ~ 0 0
=
::. ::. 0
2
.. 0
.
::.
::.
::.o
~
0
30000
cm-t
20000
,---L---
15000
y
6
ORTHOCLASE ITRONGAY
4 W U
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