402 90 198MB
English Pages 411 Year 1983
Table of contents :
Page 1
Titles
REVIEWS in
Volume 11
CARBONATES:
MINERALOGY and CHEMISTRY
RICHARD J. REEDER, Editor
The Authors:
Series Editor:
MINERALOGICAL SOCIETY OF AMERICA
Page 1
Titles
REVIEWS in MINERALOGY
Mineralogical Society of America
ii
Tables
Table 1
Page 1
Titles
CARBONATES:
MINERALOGY and CHEMISTRY
TABLE of CONTENTS
1
Chapter
CRYSTAL CHEMISTRY of the RHOMBOHEDRAL CARBONATES
Page 2
Titles
2
3
Page 3
Titles
4
5
Page 4
Titles
Fossil shells
. . . .
6
Page 5
Page 6
Titles
8
Page 7
Titles
9
Page 8
Titles
Stacking faults
Stylolites - "Pressure solution"
. ... .
R
REFERENCES
Page 1
Titles
CARBONA TES:
MINERALOGY and CHEMISTRY
FOREWORD
PREFACE and ACKNOWLEDGMENTS
iii
Page 2
Page 1
Titles
1
CR YST AL CHEMISTRY of the RHOMBOHEDRAL CARBONATES
Page 2
Page 3
Titles
l
o
3
Tables
Table 1
Page 4
Titles
h + k
h
k:
+ £
h
z
~
Tables
Table 1
Page 5
Page 6
Page 7
Titles
........... %
Page 8
Page 9
Titles
9
Page 10
Titles
Atomic thermaZ vibrations.
Page 11
Titles
11
Tables
Table 1
Page 12
Titles
12
Tables
Table 1
Page 13
Titles
StructuraZ variation.
Page 14
Titles
i;
'"
::.
N' A Zn
Mn
UNIT CELL VOLUME (1.')
'.0
·Cd
.Fe
.Zn
• Mg • Mn
2.'
~
o
14
Tables
Table 1
Page 15
Tables
Table 1
Page 16
Page 17
Titles
The magnesian calcite solid solution.
Tables
Table 1
Page 18
Page 19
Titles
.;;:r
="
.,.
~
Page 20
Titles
::bd
The CaC03-CdC03 solid solution.
The Ni-Mg carbonate soZid solution. Based on the similarity of ionic
Page 21
Page 22
Tables
Table 1
Page 23
Page 24
Titles
.,
•
~
~
o
-o
'"
~
.::
"
-o
-
o
"
~
~
o
"
'"
Il
....
u
9
o
9
0-
o
:i:
ur
~
e
.!::
:
o
.,_
'"
~
-
.~
.!::
'"
III
III
-o
OJ
OJ
24
Page 25
Titles
25
Page 26
Titles
OctahedraZ distortion.
Page 27
Titles
re
...
Table 9
Tables
Table 1
Table 2
Page 28
Titles
Thermal parameters.
Ankerite and ferroan dolomite.
Page 29
Page 30
Page 31
Titles
Kutnahorite.
Other transition metaZ doZomites.
Tables
Table 1
Page 32
Titles
Thermal disordering.
Page 33
Page 34
Page 35
Titles
Structural changes.
Disorder in low-temperature dolomites.
Page 36
Page 37
Page 38
Titles
..
~
"
.:
,.0
..
.
°0,
~o
/0
.: ° f::,
38
Page 39
Titles
::il_§:=~:
Page 40
Page 41
Titles
U H HUH H
Page 42
Titles
-:
c
Page 43
Page 44
Titles
44
Tables
Table 1
Table 2
Table 3
Page 45
Page 46
Titles
(a) Colcite- type (b) CoCO;, II
~ \ ~ \
---®----@----@----@------------~-----@---~------0-
=~
~ \ \ \
Page 47
Page 48
Page 1
Titles
2
PHASE RELATIONS of RHOMBOHEDRAL CARBONATES
Page 2
Page 3
Page 4
Tables
Table 1
Page 5
Titles
~
u
~
! + /""
j :::t~ j:"
Page 6
Titles
-
-
-
-
I
15
I
10
I
5
Solution
/.> '"
Calcite /Z~/-
Solid J/
A/
if
1'1
"
> I Calcite + Dolomite
> I
o
9001-
5001-
54
Tables
Table 1
Page 7
Titles
Relations at higher pressures and temperatures.
Page 8
Page 9
Titles
Cd+Cm
60 80 100
MgC03
Ar+Cd
20 40
00 20 40 60 80 1000
MgCO~
\
\
+
T
1500
500
1000
u
57
Tables
Table 1
Page 10
Titles
AdditionaZ considerations in subsoZidus relations.
Page 11
Page 12
Tables
Table 1
Page 13
Titles
::k XXXX
XXXX
X
x
X
Tables
Table 1
Page 14
Tables
Table 1
Page 15
Titles
•
•
•
•
•
•
,
,
,
Tables
Table 1
Page 16
Page 17
Titles
Zn-Dolomite I Zn- Dolomite
+ +
Calcite Smithsonite
Zn- Calcite
Ca - Smithsonite
T
Page 18
Page 19
Titles
I
Page 20
Titles
-----
Page 21
Titles
-----
Page 22
Page 23
Titles
._. __ _.-..CoMnco,',
"
, 'j
, ,
f .. :
,/'
71
Page 24
Titles
\
eeo-c
Page 25
Page 26
Page 27
Page 28
Page 1
Titles
3
Page 2
Page 3
Page 4
Page 5
Tables
Table 1
Page 6
Titles
..
;./:\
:",
.. '
.. \
..
... 7.\
•.. ~
..... \
. ' .. '\
. . .,: .i:-
~ .' \
. . .
_':: .. ::::: .. ::\~\~ .. ...!....OL: ., '. :., : :':': ... ".: .. : .:.:/:: .
Page 7
Titles
Co Mn (C03)2
.\
/: .
. ...
'._. .
. .
...... .
.....
... .
:
:
.. '
..
'.'
._::_.~:.!' • .:t:u_: ;M" •• " \~.:: •• ;.:: :.~(./)::; .:. :':~" ~,~ ~ :: •• .. __ --"'- __ ->
83
Page 8
Page 9
Page 10
Page 11
Titles
87
----
Page 12
Page 13
Titles
/~2~
Page 14
Page 15
Page 16
Page 17
Page 18
Page 19
Page 20
Page 1
Titles
4
MAGNESIAN CALCITES: LOW-TEMPERATURE 'OCCURRENCE,
Fred T. Mackenzie, William D. Bischoff, Finley C. Bishop,
Page 2
Page 3
Tables
Table 1
Page 4
Page 5
Titles
- TOC
o 28
24
20
16
12
8
o
WATER TEMPERATURE 'C
~
..
...
g
N
'"
101
Tables
Table 1
Table 2
Table 3
Page 6
Tables
Table 1
Page 7
Tables
Table 1
Page 8
Page 9
Page 10
Titles
.~
NBS Oolomit. __ • :/~~se~~;n~Jitl! 0
Tables
Table 1
Page 11
Page 12
Page 13
Titles
...
J
Tables
Table 1
Page 14
Tables
Table 1
Page 15
Page 16
Page 17
Titles
7.2
•
7.4
•
.,
] 76
o
o
8.2
8.4
8.6
o
11
o
10 20
MOLE %MgC03
11
30
113
Page 18
Page 19
Page 20
Titles
r ... --------1
t I - ...... _
i I ~ - · .___:».
[disordered calcite]
IT at
low P
[NaCI]
149
Tables
Table 1
Page 6
Page 7
Page 8
Tables
Table 1
Page 9
Titles
o
~
,.
Page 10
Page 11
Titles
350
300
Temperature -c
155
Tables
Table 1
Page 12
Titles
° 0
°
Page 13
Page 14
Page 15
Titles
Sr
Pb
Page 16
Page 17
Titles
Table 4. Anhydrous rhombohedral and orthorhombic carbonates
-----------------_.-------------------_ .... --_._-----------------
-_ ... ---_ ...... ".----== ..... ===-""'.,..= .... _-_ ....... =_."" ... = .. = ... "",.=--------------
--------_ .. _-----------_._--------------------_ ... _-----------------
-----------------_.-----------------------_.-----_._------.------
Recent shells.
Tables
Table 1
Page 18
Titles
Table 5. Trace element content of aragonitic skeletons.
...... _-_ ....... _-,.""---------------------- .. _---------------------------
}
u
--_ ... _------------------_._---------_._------ ... _-----._---------
:d
162
Page 19
Page 20
Titles
ionic radius (Al
Page 21
Tables
Table 1
Page 22
Titles
40
Tables
Table 1
Table 2
Page 23
Titles
Fossil ehel.l.e ,
Page 24
Titles
i
\ t
;--l-+/ "''+'"
Page 25
Page 26
Tables
Table 1
Page 27
Page 28
Titles
r : ~
.(
.. i·
Page 29
Titles
temperature (OC)
Tables
Table 1
Page 30
Page 31
Titles
b 1000 I,...,-.,---,-r-,...---,-.----,-~
CaBa(C03)2
.._
E
mole
percent
Tables
Table 1
Table 2
Page 32
Titles
Pb
Page 33
Page 34
Titles
t~ ~!
~ ~. ~I U)
'"
~~----------------------~a
Page 35
Page 36
Page 37
Titles
\
a
Page 38
Page 39
Tables
Table 1
Table 2
Page 40
Titles
3 4.0
~
cation atomic moss
'"
E
E
6.0
5.0
100
140
180
220
100
equivalent mol % SrC03
witherites
cation atomic mass
E
E
Tables
Table 1
Page 41
Page 42
Titles
aile
Tables
Table 1
Table 2
Table 3
Page 43
Page 44
Titles
-7
Page 45
Page 46
Tables
Table 1
Page 1
Titles
6
The POL YMORPHS of CaC03
and the ARAGONITE- CALCITE TRANSFORMATION
William D. Carlson
Page 2
Titles
oco, PHASE RELATIONS
Page 3
Page 4
Titles
0' 'j»ti:)J-'¥" lor 'V' 'Ol' '°1°' I!!)r
350 400 450 500 550
16 [ ContOU'S on Sr-rich limit of
:012
W
~8
~6
194
Page 5
Page 6
Page 7
Titles
lii
rJ
1", T "1
--- - -X-X'-_1
. \
,
t
Tables
Table 1
Table 2
Table 3
Page 8
Titles
Evidence for disordering.
Page 9
Titles
- ~ .. ,\.
ON.
199
Tables
Table 1
Page 10
Titles
Possible disordering schemes.
Page 11
Page 12
Titles
The transformation under conditions of aragonite stability.
Page 13
Titles
The transformation outside the aragonite stabiZity fieZd. Experiments
Page 14
Titles
Petrographic observations.
Experiments measuring buZk transformation rates.
Page 15
Titles
"
.~
_.> e
o 0
..,
"' ...
e.!l
o
~.&
~.s
.. "
...
" ..
..
~ §
...
.. '"
.. ~
.... '"
Page 11
Titles
Dislocations.
Page 12
Page 13
Titles
361
Page 14
Titles
"
j
~ ....
~o
e
"
-e
e
o
.....
"''''
~::!
"'"
.!1
REVIEWS in MINERALOGY Volume 11
CARBONATES: MINERALOGY
and CHEMISTRY
J.
RICHARD
REEDER, Editor
The Authors: DAVID J. BARBER
FRED T. MACKENZIE
Dept. of Physics University of Essex Colchester, England
JANE SCHOONMAKER C04
3SQ
WILLIAM D. BISCHOFF
Dept. of Oceanography University of Hawaii Honolulu, Hawaii 96822
FINLEY C. BISHOP
JOHN
Dept. of Geological Sciences Northwestern University Evanston, Illinois 60201
Dept. of Oceanography Texas A & M University College Station, Texas 77843
W. MORSE
WILLIAM D. CARLSON
RICHARD
Dept. of Geological Sciences University of Texas at Austin Austin, Texas 78712
Dept. of Earth & Space Sciences State University of New York Stony Brook, New York 11794
J. REEDER
ERIC J. ESSENE
J. ALEXANDER
Dept. of Geological Sciences University of Michigan Ann Arbor, Michigan 48109
Dept. of Geological Sciences Virginia Polytechnic Institute State University Blacksburg, Virginia 24061
JULIAN
SPEER &
R. GOLDSMITH
Dept. of Geophysical Sciences University of Chicago Chicago, Illinois 60637 MICHELE
LOIJENS
ROLAND
WOLLAST
HANS-RUDOLF
Laboratoire d'Oceanographie Universite Libre de Bruxelles 1050 Brussels, Belgium
Series Editor: Virginia
JAN VEIZER Dept. of Geology University of Ottawa Ottawa, Ontario, Canada
KIN 6N5
WENK
Dept. of Geology & Geophysics University of California Berkeley, California 94720
PAUL H. RIBBE Dept. of Geological Sciences Polytechnic Institute & State University Blacksburg, Virginia 24061
MINERALOGICAL
SOCIETY OF AMERICA
COPYRIGHT MINERALOGICAL
1983
SOCIETY
PRINTED
of AMERICA
BY
BookCrafters, Inc. Chelsea, Michigan 4-8118
REVIEWS in MINERALOGY (Formerly:
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NOTES)
ISSN 0275-0279 Volume
11:
CARBONATES:
MINERALOGY
and CHEMISTRY
ISBN 0-939950-15-4-
those
ADDITIONAL listed below
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SULFIDE MINERALOGY, P.H. Ribbe, editor
(1974) (1975; revised 1983)
284 p.
2
FELDSPAR MINERALOGY, P.H. Ribbe, editor
3
OXIDE MINERALS, Douglas Rumble III, editor
4
MINERALOGY and GEOLOGY of NATURAL ZEOLITES, F.A. Mumpton, editor (1977)
232 p.
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ORTHOSILICATES, P.H. Ribbe, editor
450 p.
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MARINE MINERALS, R.G. Burns, editor
7
PYROXENES, C.T. Prewitt, editor
8
KINETICS of GEOCHEMICAL PROCESSES, A. C. Lasaga and R.J. Kirkpatrick, editors (1981)
(1976)
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(1980)
9A AMPHIBOLES and OTHER HYDROUS PYRIBOLES - MINERALOGY, D.R. Veblen, editor (1981)
362 p. 502 p.
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9B AMPHIBOLES: PETROLOGY and EXPERIMENTAL PHASE RELATIONS, D.R. Veblen and P.H. Ribbe, editors (1982) 390 p. 10 11
CHARACTERIZATION of META}IORPHISMthrough MINERAL EQUILIBRIA, J.M. Ferry, editor (1982) CARBONATES,
R.J. Reeder, editor
ii
(1983)
397 p.
CARBONATES: MINERALOGY
and CHEMISTRY
TABLE of CONTENTS COPYRIGHT;
LIST OF PUBLICATIONS
FOREWORD PREFACE;
Page ii
......•.
iii
ACKNOWLEDGMENTS
iii Chapter
1
CRYSTAL
of the RHOMBOHEDRAL
CHEMISTRY
INTRODUCTION
1
RHOMBOHEDRAL
VERSUS HEXAGONAL
THE C03 GROUP AS A STRUCTURAL
AXIAL SYSTEMS
2
UNIT
4
THE R3c CARBONATES
6
The calcite structure Calcite isotypes
6 8
Atomic thermaZ vibrations Structural variation Solid solutions of R3c carbonates The magnesian calcite soZid solution The CaC03-CdC03 solid solution The Ni-Mg carbonate solid solution Lattice
parameters
THE R3 CARBONATES The dolomite
in other solid solutions
Dolomite
22 23 26 28 28 28 31 31 32 32 32 35 35 37
isotypes
carbonates
Thermal disordering Structural changes Disorder in low-temperature dolomites Lattice
parameters
of dolomite-type
OTHER DOUBLE
CARBONATES
•
carbonates
40
AT HIGH TEMPERATURES
AND PRESSURES
Thermal expansion High-temperature transformations CaC03(II) structure
of calcite
FOR FUTURE WORK
ACKNOWLEDGMENTS
17 17 20 20 21 22
Calcian dolomites and ankerites Cation order in dolomite-structure
SUGGESTIONS
14
structure
Ankerite and ferroan dolomite Kutnahorite Other transition metal dolomites
CHEMISTRY
10
. . • . . • •
Interatomic distances Octahedral distortion Thermal parameters
CRYSTAL
CARBONATES
J. Reeder
Richard
43 43 45 45 46
. • . . • .
47 v
Chapter
2
PHASE RELATIONS
2
of RHOMBOHEDRAL Julian
CARBONATES
R. Goldsmith Page
INTRODUCTION
AND EXPERIMENTAL
THE END-MEMBER DOLOMITE-TYPE BINARY
RESULTS
49
CARBONATES
51
COMPOUNDS
PHASE
51
RELATIONS
51
CaC03-MgC03
Relations at moderate pressures Relations at higher pressures and temperatures Additional considerations in subsolidus relations CdC03-MgC03 CaC03-MnC03 CaC03-FeC03 Additional binary
joins with
a single
solvus
CaC03-NiC03; CaC03-CoC03; MgC03-NiC03 Binary joins with extensive solid solubility The join CaC03-ZnC03 and Zn-dolomite A note on the asymmetry of the solvi TERNARY
PHASE
RELATIONS
66
CaC03-MgC03-FeC03 CaC03-MgC03-MnC03 Order-disorder relations in Fe- and Mn-containing dolomites The systems CaC03-MgC03-CoC03 and CaC03-MgC03-NiC03 SUGGESTIONS
FOR FUTURE
ACKNOWLEDGMENTS
51 51 55 58 60 60 62 63 63 64 64 65
WORK
66 70 70 72
75
. . . . . .
76 Chapter
3
SOLID SOLUTIONS and SOLVI among METAMORPHIC CARBONATES with APPLICATIONS to GEOLOGIC THERMOBAROMETRY
3
Eric J. Essene
INTRODUCTION
77
EXPERIMENTAL
DATA BASE
77
DETERMINATION
OF CARBONATE
COMPOSITIONS
78
COMPOSITIONS
OF METAMORPHIC
CARBONATES
80
Rhombohedral Orthorhombic SOLVUS
LIMITS
Solvi Solvi APPLICATIONS
carbonates carbonates
IN METAMORPHIC
in the system in the system
81
84 CARBONATES
CaC03-MgC03-FeC03 CaC03-MgC03-MnC03
OF CALCITE-DOLOMITE
Regional metamorphic Contact metamorphic THE ARAGONITE-CALCITE
. •
THERMOMETRY
rocks rocks
TRANSITION
85 85 86 88 89 91
AS A THERMOBAROMETER vi
93
CHAPTER 3, continued COEXISTING
ORTHORHOMBIC
SUGGESTIONS SUMMARY
Page AND RHOMBOHEDRAL
CARBONATES
94
FOR FURTHER WORK
95
..
95
ACKNOWLEDGMENTS
96 Chapter
4
MAGNESIAN
CALCITES:
SOLUBILITY Fred T. Mackenzie, Michele Loijens,
4
LOW-TEMPERATURE
and SOLID-SOLUTION
OCCURRENCE, BEHAVIOR
William D. Bischoff, Finley C. Bishop, Jane Schoonmaker & Roland Wollast
INTRODUCTION
97
LOW-TEMPERATURE
OCCURRENCE
98
Skeletal magnesian calcites Magnesian calcite cement UNIT CELL PARAMETERS: High-temperature
98 98
BIOGENIC AND SYNTHETIC INORGANIC PHASES.
. • ..
synthetic materials
104 104 105 107 108
Synthesis techniques Unit cell parameters Low-temperature synthetic materials Biogenic materials SOLUBILITIES
AND SOLID SOLUTION BEHAVIOR
Solubilities
of magnesian
ll2
calcites
114 114 118 118 119
Dissolution experiments Precipitation experiments Interpretation of experimental data Theoretical
considerations
ThermodYnamic equilibrium Stoichiometric saturation Experimental tests of stoichiometric saturation Expression of solubility
120 124 126 127
Evaluation of thermodynamic properties from dissolution experiments Other approaches to estimation of magnesian calcite properties
Solid solution properties Estimation of free energy of mixing from high-temperature data Estimation of excess lattice energy Evaluation of the heat of mixing by calorimetric measurements Hypothesis
of an hydrated magnesian
SOME CONCLUDING
REMARKS
ACKNOWLEDGMENTS
. . . . CRYSTAL
129 132
132 135 136 138
calcite
140 142 144
Chapter
5
104
5
CHEMISTRY and PHASE RELATIONS ORTHORHOMBIC CARBONATES J. Alexander
of
Speer
INTRODUCTION
145
CRYSTALLOGRAPHY
145
vii
CHAPTER 5, continued
Page
Crystal structures Charge distribution AC03 polymorphism Twinning Morphology The CaBa(C03)2 phases Carbocernaite CHEMISTRY
145 150 151 152 152 154 157
. . . . .
158
Inorganic orthorhombic carbonates Biogenic orthorhombic carbonates Recent she l.le Fossil shells ISOTOPIC
158 161 161 167
COMPOSITION ..
169
Dependence Dependence Dependence
on crystal chemistry on physical conditions on source
PHASE RELATIONS
.
170 170 171
.
.
Unary systems Binary systems
177 minerals
OCCURRENCE OF ORTHORHOMBIC CARBONATES AND DISCUSSION COMPOSITIONS AND MINERAL ASSEMBLAGES PHYSICAL PROPERTIES
178 OF THEIR
. .
182 184 185 188 188 188
FOR FUTURE WORK . .
189 Chapter
6
178 182
Density Lattice parameters Optical properties Luminescence Magnetic properties Infrared and Raman spectra SUGGESTIONS
171 171 173 173 174 174 174 175 175 176
CaC03-SrC03 CaCOrBaC03 CaCOrPbC03 SrC03-BaC03 SrC03-PbC03 BaCO 3-PbCO 3
Ternary systems Phase relations in aqueous systems Phase relations involving noncarbonate
.
6
The POL YMORPHS of CaC03 and the ARAGONITE--CALCITE
TRANSFORMATION
William D. Carlson INTRODUCTION THE POLYMORPHS
191 OF CALCIUM CARBONATE
191
The calcite-aragonite equilibrium CaC03(II) and CaC03(III) CaC03(IV) and CaC03(V) The role of rotational disorder of C03 groups Evidence for disordering viii
193 195 196 198 198
CHAPTER 6, continued
Page
Possible disordering schemes Speculations on disorder in CaC03 as a function of pressure and temperature ARAGONITE-CALCITE
TRANSFORMATIONS
The ca1cite-to-aragonite
IN THE SOLID STATE
The transformation under conditions of aragonite stability The transformation outside the aragonite stability field transformation
Petrographic observations Experiments measuring bulk transformation rates Independent determination of growth rates Extraction of nucleation rates from bulk transformation rates Summary THE ARAGONITE-CALCITE Observational
TRANSFOR}~TION
IN THE PRESENCE OF WATER . . . ..
evidence for the nature of the aqueous transformation
Marine environments Fresh water environments Mechanisms
of the transformation
Dissolution at surface of parent crystal Nucleation of product crystal Transport of complexes in solution Precipitation at surface of product crystal Interpretation mechanisms
of natural occurrences
211 212 212 212 213 214 214 214 214 215
attempts to quantify reaction kinetics
The significance of transport processes The time dependence of the overall transformation Inconsistency of a time-squared volume dependence with other observations A possible explanation for the time-squared volume dependence CONCLUSIONS
202 202 203 203 204 204 207 207 209
in terms of reaction
Reasons for extremely limited extent of transformation in sea water Reasons for apparent differences in transformation type Reasons for oriented overgrowths and topotaxial replacement Reasons for selective transformation of skeletal materials Reasons for long-term preservation in ancient limestone Experimental
201 202
transformation
The aragonite-to-ca1cite
200
AND OPPORTUNITIES
FOR FURTHER RESEARCH
. . . . . . . . ..
ACKNOWLEDGMENTS
215 215 217 218 218 219 219 219 220 222 224 225
7
Chapter
The KINETICS of CALCIUM CARBONATE
7 DISSOLUTION and PRECIPITATION
John W. Morse INTRODUCTION
227
BASIC PRINCIPLES
228
REACTION KINETICS
231
IN SIMPLE SOLUTIONS
231 231 234
Dissolution
General observations Models and mechanisms ix
CHAPTER 7, continued
Page
Precipi tation
238
General observations and models Secondary nucleation
238 239
DISSOLUTION AND PRECIPITATION REACTIONS OF NONBIOGENIC CARBONATES IN COMPLEX SOLUTIONS . . . . . . . . . . . . . . . . . . . . . . .. General considerations
Major influences Models for reacting surfaces and inhibitors Individual seawater-component
241 242
influences
244
Magnesium Sulphate
244 246
Reaction kinetics
in seawater and related solutions
246
Dissolution Precipitation
246 247 249
Other specific influences
Phosphates Heavy metals Organics
249 252 253
SPECIFIC TOPICS . . . .
254
Biogenic carbonate dissolution kinetics
254 254 256 258 261 261 262
General considerations Influence of grain size Prediction of solubility from kinetics Kinetic influence on coprecipitation
reactions
Experimental methods Cation coprecipitationwith calcite ACKNOWLEDGMENTS
264 Chapter
8
TRACE
241 241
ELEMENTS
and ISOTOPES
8
in SEDIMENTARY
CARBONATES
Jan Veizer
INTRODUCTION INCORPORATION
265 OF TRACE ELEMENTS INTO CARBONATE MINERALS
INCORPORATION OF STABLE ISOTOPES OF OXYGEN AND CARBON INTO CARBONATE mNERALS Theoretically predicted composition of carbonate minerals Isotopic variations in natural waters Isotopic composition of natural carbonates INCORPORATION
OF RADIOGENIC
Radiocarbon U-series disequilibrium Isotopes of strontium DIAGENETIC REPARTITIONING RECORD OF TERRESTRIAL
ISOTOPES INTO CARBONATE MINERALS.
267 271 272
276 278 279 279 282 284
nuclei
OF TRACERS
285
EVOLUTION IN ANCIENT CARBONATES
Oxygen isotope paleothermometry Post-Triassic paleoceanography Carbon isotopes of ancient oceans: the story of life Strontium isotopes and buffering of the oceans x
288 289 289 292 294
CHAPTER 8, continued
Page
Oxygen isotopic composition of sedimentary Secular variations in chemical composition CONCLUDING
carbonates of carbonates
299
REMARKS
ACKNOWLEDGMENTS
300 Chapter
9
296 298
MICROSTRUCTURES Hans-Rudolf
9 in CARBONATES
Wenk, David J. Barber
& Richard
J. Reeder
INTRODUCTION
301
ORIGINS OF MICROSTRUCTURES
303
Deformation microstructures Transformation microstructures Growth microstructures
303 306 3ll 3ll 3ll 313 313 313
Dislocations Growth bands Faults Stacking disorder Twins METHODS OF ANALYSIS
. . . .
313
Scanning electron microscopy (SEM) Transmission electron microscopy (TEM) Scanning transmission electron microscopy (STEM) High resolution electron microscopy (HREM) POLYMORPHIC
TRANSFORMATIONS
. . . . . .
Cation ordering in dolomite Aragonite ~ calcite transformation
Observations in sedimentary rocks Observations of the solid state transformation in the TEM VARIATIONS
IN STACKING ORDER
• . . . . . . . . . . . . • .
Periodic basal superstructure in dolomite Stacking disorder and polytypes in rare earth carbonates MODULATED
STRUCTURES
PARALLEL TO r
=
{1014} . . . . . . . . .
322 326 328 328 329 332
352 352 354
. . . . . .
Deformation
319 321
352
CARBONATES
Recent dolomites Magnesian calcites DEFORMATION
319
332 338 343 344 348
Calcian dolomites Saddle dolomites Calcite Carbonatites Interpretation OTHER SEDIMENTARY
314 315 317 318
354 355 356 357 359
mechanisms
Calcite Dolomite The effects of twinning
Biaxiality
xi
CHAPTER
9, continued
Other defects
in deformed
Page carbonates
Dislocations Stacking faults Stylolites - "Pressure solution" ACKNOWLEDGMENTS
R
.
. . . . . .
REFERENCES
xii
...
.
359 359 360 364 367
369
CARBONA TES: and CHEMISTRY
MINERALOGY
FOREWORD This is Volume 11 of REVIEWS in MINERALOGY, Course Notes" for the Mineralogical of the mineralogy the M.S.A.
and chemistry
of carbonates
in 1974.
This review
appears just four years after
Short Course on Marine Minerals which covered marine manganese
oxides and iron oxides, barite,
a series begun as "Short
Society of America
evaporite,
silica polymorphs,
and placer minerals.
Volume 6, Marine Minerals,
because,
coverage
mineral
of this important
and the zeolite, clay, phosphorite, Carbonates were not included in
as editor Roger Burns put it, " ... group warrants
a separate monograph."
Several years ago, Rich Reeder, who was and still is very excited about new vistas
of research
tron microscope bonates
centered around application
to carbonates,
volunteered
for the Mineralogical
Society of America.
by this volume with its fifteen authors, 1983, just prior to the annual meetings of America
at Indianapolis,
of the transmission
to organize
elec-
a short course on car-
His success is commemorated
nine of whom lectured October of M.S.A. and the Geological
28-30,
Society
Indiana. Paul H. Ribbe Blacksburg, VA September 1, 1983
PREFACE and ACKNOWLEDGMENTS This volume of Reviews in Mineralogy understanding
attempts
to synthesize
our present
of certain aspects of the mineralogy
and chemistry
of the rock-
forming carbonates. of research. mentary)
Hopefully,
it reflects
the presently
more active areas
This review follows, by ten years, a major assessment
carbonate
minerals
of subject material,
by Lippmann
(1973).
of (sedi-
There is only minor overlap
and I hope that this difference
reflects
fairly how this
field has developed. In some respects mineral chemical
carbonates
groups providing processes
lative importance
an abundant
throughout
Moreover
record of biological,
much of geologic
in sedimentary
more emphasis here.
are unique, for they are one of the few
time.
rocks, low-temperature
the obvious iii
correlation
physical,
Because
and
of their re-
examples
are given
with energy resources
has been a significant terest in this area. reflection
factor contributing However,
of their widespread
vironments,
including
to the current resurgence
the broader
interest
occurrence
metamorphic
in carbonates
in vastly different
and igneous settings,
ciation of their role in both atmospheric
of in-
is also a
geologic
en-
as well as an appre-
and oceanic chemistry,
both past
and present. In this volume, crystal chemistry
some of the papers are general
and phase relations),
damental
nature and are of interest
coverage
and generally
geochemistry. a relatively
reflect
and they provide overviews
to many.
new and powerful in carbonate
technique
approaches
The various efforts.
A hurried
all gratefully
schedule,
these should be brought
for mineralogical
ways; in particular
however,
without
I thank my friends and colleagues
errors
in their to persist;
Sarah Vaughan,
the cooperation
Polytechnic
and
in various
at the State University
Support in various but essential
the final product.
torial assistance
were expeditious
Many others contributed
thanks go to Paul H. Ribbe for advice,
Ada Simmons,
of manuscripts
in this volume is still "fresh."
allows for unnoticed
all of whom I thank.
vided both by SUNY and by Virginia
for producing
that has
to my attention.
of New York at Stony Brook.
Special
research
the completion
acknowledged,
This volume would not have been possible help of the authors,
electron microscopy,
research.
much of the newer material
reviewers,
Institute reviews,
forms was pro-
and State University. copy editing,
Typing of the final manuscript
Theresa Beddoe and Margie Strickler,
and
was done by with edi-
by Julie Anne Ribbe. Richard J. Reeder Stony Brook, NY September 1, 1983
SPECIAL ACKNOWLEDGMENT The Mineralogical Company,
Society
of America
ARCO Oil and Gas Company,
for providing
in
used in carbonate
transmission
Owing to the short time interval between and publication,
of a fun-
Others are more specialized
the different
The final chapter introduces
great potential
(i.e., those addressing
scholarships
for graduate
is grateful
and SHELL Development students
carbonates.
iv
to AMOCO Production
to attend
Corporation
the Short Course on
1
CR YST AL CHEMISTRY
of the RHOMBOHEDRAL
CARBONATES
Richard J. Reeder INTRODUCTION Crystal minerals, whether
chemistry plays an important role in understanding
both in terms of reactivity
and stability.
in the solid state or in aqueous
Stability
preting
the potential
structure
differences
Crystal growth processes,
imposed by coordination
among natural minerals,
for chemical
and bonding,
properties.
A multitude
is available
to study these, but in all cases the essential
understanding
of the crystal structures
The history carbonates
of crystal structure
of calcite was firmly established that of dolomite Merwin
(1924).
sophisticated precise
Accurate
determinations
element is an
of the common rhombohedral
sporadic in nature.
The general structuI
early in the century by Bragg
just ten years later by Wasastjerna structural
data collection
refinements
methods,
of positional
in
of techniques
involved.
investigations
has been long and somewhat
and
so important for inter-
change, reflect detailed differences
as do physical
of
systems, are influenced by the arrangE
ment of atoms in the crystal and the constraints bonding.
the behavior
(1914), and
(1924) and Wyckoff and
awaited the development
and by 1965, studies had yielded
and thermal parameters
for calcite
of more fairly (Sass
et al., 1957; Inkinen and Lahti, 1964; Chessin et al., 1965) and dolomite (Steinfink and Sans, 1959).
Lippmann
at that time, giving a more complete tinued interest
(1973) thoroughly historical
in carbonate minerals
recent studies; The preferred although
carbonates.
have been undertaken
transmission
have been used (see Chapter
based on the more
to much of the older work, see Lippmann
technique for structural
Raman) of carbonates
for most of the com-
The present review is primarily
for references
recently
Since then, con-
has fostered many new crystal structure
studies, and today modern refinements mon rhombohedral
reviewed data available
development.
studies has been x-ray diffraction,
electron microscopy
9).
(1973).
and electron diffraction
Studies of the vibrational
have been reviewed by White
spectra
(IR and
(1974) and Scheetz and White
(1977) • Of the rock-forming accounting
carbonates,
calcite and dolomite are the most abundant
for more than 90% of natural
carbonates.
The structure
of calcite
is descriptively
fairly simple, and it is the same as that taken by several
other anhydrous,
single carbonates
rhodochrosite
(MnC03), otavite
(CoC03), and gaspeite Single carbonates
(NiC03).
including magnesite
(CdC03), smithsonite
(MgC0 ), siderite (FeC0 3 3 (ZnC0 ), sphaerocobaltite 3
with cations larger than Ca2+ form with the orthorhombic
aragonite
structure. The explanation given for this preference usually relates 2 to the size of Ca +, which is near the limit for 6-fold coordination. In the
aragonite however,
structure,
the cat-ion is 9-coordinated.
that at high temperatures
invert to a rhombohedral,
the orthorhombic
calcite-like
RHOMBOHEDRAL
structure
VERSUS HEXAGONAL
When dealing with the rhombohedral either a rhombohedral
or hexagonal
It is interesting BaC0
and SrC0
3
3
(Chang, 1965). AXIAL SYSTEMS
carbonates,
axial system.
smallest unit cells for both calcite and dolomite hedrons
carbonates
to note,
one has the choice of using It should be noted that the
are acute primitive
rhombo-
(Fig. 1) with cell contents of 2 CaC0
and 1 CaMg(C0 )2' respectively. 3 3 Rhombohedral cells are described entirely by two parameters -- a , the edge r length, and ~r' the angle between any two of the three equal length edges forming the apex of the rhomb.
Since the line connecting
the apices of the rhombo-
hedron is a three-fold
axis, all lattice points of the rhombohedron
equally well described
using a hexagonal
have two possible
orientations
axial system.
with respect
can be
The rhombohedron
to the hexagonal
may
axes called the
obverse and the reverse settings (International Tables for X-ray Crystallography, Vol. I).
The obverse setting shown in Figure 2 is now standard.
both calcite and dolomite,
the heights of the hexagonal
for the acute rhombohedral
cells, although
respectively,
In
cells are the same as
they contain 6 CaC0
3
and 3 CaMg(C0 ); 3
and are triply primitive.
The primary advantage tion of the axes relative
of the hexagonal
with respect to one another, and all lie perpen-
0
dicular to the c axis.
The three a axes, of equal length,
to one another.
intersect at angles of 120
This arrangement
makes it relatively
geometric aspects of the crystal structure, tinct levels along the c axis. hedral axes, particularly
especially
easy to visualize
planar features at dis-
This becomes rather awkward using the rhombo-
so when comparing
angle between axes changes from one mineral Modern descriptions
axial system lies in the disposi-
of rhombohedral
different minerals because the to the next.
carbonates
are given almost exclu-
sively in terms of the hexagonal
cell.
uses a rhombohedral
which may be based on either the true unit
description,
cell or the morphologic
Much of the older literature,
cell (also called a cleavage cell).
however,
The latter (shown
in Fig. 3) should be avoided since it is not a correct unit cell.
A proper
morphologic
unit cell does exist, but its a cell edge is twice that of the
morphologic
cell shown in Figure 3, and its cell contents are 16 times that of
the acute rhombohedral
cell.
Owing to the presence
of the fourth axis
2
(as) used in the hexagonal
axial
Figure 1 (to the left). Schematic illustration of the true rhombohedral unit cell for calcite containing 2 CaCO). The apical angle a is 'V 46° for this acute rhombohedron. Closed circles represent Ca positions; two C03 groups are shown. After Lippmann (1973)"
l 5
Figure
4
obverse lation view, X-ray
3 2
2 (below). Illustrations showing the setting of the rhombohedron in reto the hexagonal unit cell: (a) side (b) plan view. From Int'l Tables for Crystallography, Vol. I.
o
b.,
a
.~
.j '0
'0
'0
.~ .j '0
.: .j ,0
1
0
·i
+x,
-yo .j
aR
.~
.~ •j
= 46' 07"
«« = 101' 55"
Figure 3. Schematic illustration ahowf.ng the relationships between the true rhombohedral unit cell (the acute rhombohedron) and the morphologic (or cleavage) cell in calcite. Notice that the true cell is doubled in height with respect to the morphologic cell. The hexagonal unit cell is also shown. From Hurlbut and Klein (1977)"
3
.j
system, four-symbol h + k + i writing
=
0,
indices should be used -- h k i £, where
Miller-Bravais
Although
some authors prefer to drop the superfluous
indices, its presence
leaves no doubt that hexagonal
i when
indices are in
fact being used, The following and rhombohedral h k h
k:
r
- £
r
expressions
h
r
between hexagonal
Transformations
r
for fractional
2/3 hh+ 1/3 kh + 1/3 £h
r
k
r
+ kr + £
r
are useful when converting
indices:
r
-1/3 hh+ 1/3 kh + 1/3 £h
zr
-1/3 hh- 2/3 kh + 1/3 £h
atomic coordinates
between
the two systems
are as follows: xh
=
2/3 xr - 1/3 Yr - 1/3 zr
x
r
=
Yh
=
1/3 xr + 1/3 Yr - 2/3 zr
Yr
=
-xh + Yh + zh
zh
=
1/3 xr + 1/3 Yr + 1/3 zr
Z
=
- Yh + zh
Cell parameters
r
xh
+ zh
can be related by the following
conversions:
~
2a
r
sin
2r
a
r
(3a 2 h
= 1/3
+ c2)
2 h "
~ sin....!. = a /2a 2 h r All descriptions
in the present
chapter will refer to the hexagonal
unit
cell. THE C03 GROUP AS A STRUCTURAL
UNIT
The C03 group is the fundamental chemical unit from which the carbonate minerals derive their identity, This anion is also present in some minerals that might not be best described
as carbonates,
scapolite being a good example,
There in fact exists a large number of minerals where the C0 several anions
(or polyanions)
in the structure.
common "other" anion in these mixed-anion Despite
the wide variety of carbonate
Hydroxyl
group is one of 3 is perhaps the most
carbonates, mineral
structures,
the basic con-
figuration cases,
of the C03 group is found to be remarkably uniform in all but a few In its general form the C03 group resembles an equilateral triangle with
oxygen atoms at the corners and a carbon atom in the center, figuration
is attained
in calcite and its isotypes, where the local point sym-
metry of the group is 32, (6m2) characterizes
This exact con-
Zemann
(1981) notes that a higher point symmetry
one of the two distinct C03 groups in fairchildite 4
(K Ca 2
(C0 )2)' although the structure of the group is essentially identical with that 3 in calcite. Slight deviations from this form reduce the point symmetry below that in calcite, and reflect
differences
in coordination
or electronic
environ-
ment. Zemann
(1981) has compiled recent structural
data for C0 groups in 30 dif 3 He found the mean value for the O-C-O angle to be
ferent carbonate minerals. 120
in agreement with the ideal value.
0
rather small, and the great majority
o-c-o
angle approximates
large deviations
Deviations
of carbonates
from this are generally have C0
groups where the 3 In a few minerals,
the ideal value rather closely.
may be found
(up to 11
in one case), but seem to occur only
0
where the edge of a C03 group is shared with an edge of a coordination polyhedron of an adjacent cation. In acid carbonates, such as NaHC0 and KHC0 , 3 3 the o-c-o angles (now for an HC03 radical) are found to deviate from 1200 by several degrees. Zemann found the mean
between
son is provided
bond length to be 1.284
by the x-ray structural
calcite, magnesite, structural
siderite,
A
on the
c-o
result of the short
Tabulated
c-o
but quite small variation.
values range
A very useful compariet al. (1981) for
and smithsonite.
of the
Within this iso-
A,
bond length is only 0.005
Thus the effect of different
bond length within this structure
c-o
with a standard devia-
data of Effenberger
rhodochrosite
series the maximum variation
a clearly measurable cations
c-o
A
for average values in a C03 group. 1.25 and 1.31 A in all but a few extreme cases.
tion of only 0.004
type is minimal.
bond length is a rather close approach
1he
for oxygen atoms
the C03 group -- 2.22 A. Slightly shorter nonbonding 0 ..•0 distances are known for NaN03 and stishovite (cf. Table 5 of Shannon and Prewitt, 1969).
within
to the C03 group, the c-o bond lengths in the acid carbonates within individual HC03 ions. Sass and Scheurman (1962) rep or bond lengths of 1.346, 1.264, and 1.263 for NaHC03. In contrast
vary considerably
A
In those carbonates
where layers of C03 groups separate layers of dLf f eren: cation types, the carbon atom is displaced from the plane formed by the 3 oxygel atoms.
Dolomite,
with its two distinct cation layers,
Recent x-ray structural show displacements Althoff,
refinements
A
1977) appears
is reported
of ordered dolomites
of 0.018, 0.020, 0.022 and 0.027 to be somewhat
more typical for dolomite. by Knobloch
serves as a good example
A.
(see Table 8 below) The latter value (from
large, and the other values are perhaps
In buetschliite et al. (1980).
K2Ca(C03)2' The direction
a displacement
of the displacement
always toward the layer of cations with the smaller radius. position
of unlike cation layers forms an ordered
displacement
is sensitive
is
Since the juxta-
superstructure,
to the degree of cation ordering. 5
of 0.038
the average
For dolomite,
Reeder and Wenk
the deviation
(1983) have shown that the magnitude as cation disorder
ment decreases
the C0
reinforced
3 by consideration
in calcite
of the
c-o
(Peterson et al., 1979) and dolomite data) show a buildup
0, supporting
this view.
In general,
than any other M-O bond typically bond strength calculated
When we consider
the
c-o
density dis-
(Effenberger
et al.,
In calcite,
Brown-Shannon
strongE
for examplE method
(Bro.
four times greater than for the Ca-O bond. in the calcite structure
section, it will become clear that the excellent to this substantial
is
regarded as
bond will be considerably
using the empirical
atomic positions
to
of charge density between C and
found in carbonates.
and Shannon, 1973) is approximately
attributed
where
Such a viewpoint
Recent studies of electron
unpublished
c-o
unit.
bond, which is generally
in character.
1983; Reeder,
the
displace-
in most carbonates
of bond lengths and angles, it is reasonable
group as a fairly rigid structural
being strongly covalent tribution
of the average
However
occurs it is quite small.
Based on the uniformity consider
increases.
difference
in the following
cleavage can, in part, be
in bond strengths.
The cleavage
plane, {10I4}, is one that breaks the least number of Ca-O bonds and no
c-o
bonds. Several authors have considered (Effenberger
the charge distribution
et al., 1981; Yuen et al., 1978; and references
there is much disagreement
in earlier
studies, Yuen et al. and Effenberger
al. find point charges of approximately for single rhombohedral
in the C03 group therein). While et
+1 and -1 for C and 0, respectively,
carbonates. The R3c CARBONATES
The calcite structure Traditionally structure
the calcite structure has been described
as a starting point.
The primitive
cubic NaCl structure is a rhombohedron
using the NaCl
unit cell of the face-centered
whose 3-fold axis is coincident
the 3-fold axis of the cubic unit cell (i.e., the body diagonal), volume is one quarter of the latter.
with
but whose
If Na atoms are replaced by Ca atoms
and Cl atoms by C03 groups, a structure somewhat resembling calcite results. By necessity, the rhombohedron must be compressed in a relative sense along the 3-fold axis to accommodate
the "flat" C0
3
groups now lying perpendicular
to this axis. At once we see the limitations spherical
symmetry, being centers of symmetry
C03 groups are triangular. successive
of this description.
carbonate
The different
layers are nowhere 6
The Cl atoms have a
in the NaCl structure, while the
orientations
foreshadowed
of the C03 groups in in the NaCl structure.
z:
Figure 4 (to the left). Schematic illustration of the hexagonal unit cell of calcite, a ""4.99 a = 17.06 Ca atoms are open circles; CO) groups are triangles; z. coordinates for Ca layers are shown on the right. From Lippmann (1973) .
1.
........... %
A.
..........%=213
.............. 3/6= 1/2
Figure 5 (above). The CO) layer in calcite as seen down the c axis. The CO) groups have identical orientations throughout the layer. Dashed circles show the positions of Ca atoms projected from the cation layer above the CO) plane. Relative sizes of the Ca and 0 circles correspond to crystal radii as assigned by Shannon and Prewitt (1969).
In fact, we will see that the rhombohedral
cell derived from the NaCl structure
is not a proper unit cell for calcite. Figure 4 shows a schematic model for the calcite structure.
It can be seen
layers along the c axis.
that layers of Ca atoms alternate with carbonate
The
C0
groups have like orientations within each layer, but reversed orientations 3 in successive layers. Thus the translation along c to similarly oriented C03 layers is doubled
ture.
in comparison
This requires Perhaps
a doubling
to the analogous
a better description
of the oxygen atoms are teferred Megaw, 1970, 1973).
translation
in the NaCl struc-
of the unit cell height as shown in Figure 3. of the structure
is provided
to a pattern of hexagonal
While only approximate,
if the positions
close packing
(cf.
this analogy does show the orien-
tational relationships
among C03 groups in successive layers. Within a given layer of hexagonally-packed oxygens, carbon atoms are introduced such that each
oxygen coordinates
with only one carbon reSUlting
of C in that layer.
in a hexagonal
Calcium atoms then fill those octahedral
(between oxygen layers) that avoid coordination
distribution
intersticies
with two oxygens of the same
C0
group, since that 0-0 distance would be very short (Fig. 5). C atoms in 3 successive oxygen (or C03) layers are distributed so as to avoid superposition over either Ca or C atoms in adjacent cation and C03 layers. This ensures that Ca is then coordinated to six oxygens, each belonging to different C03 groups. The unit translation
along the direction 7
of stacking
(i.e., along the c axis)
Table I.
Fornal
description
of calcite
is equivalent
structure
to the height of six C0
3
layers.
Ce11 parameters':
Atom
pos i t Ions
In reality,
R3c (No. 167) Hexagonal. rhombohedrally-centered 6 CaC03
Space group: Unit cell: Cell contents:
s ":
the oxygens are not
closest packed, and in fact, the ideal hexagonal pattern
a = 4.9896 j\ C =17.0610 j\
is not attained owing
to the foreshortening
Ca in 6 (b): 0, 0, 0 C in 6 (a): 0,0, Ii o in 18(e): x , 0, Ii x = 0.2568
*Cell parameters for other calcite carbonates are given in Table 2.
different C03 groups are 3.19 K (across C03 planes) and 3.26 A (in-plane), both
structure
considerably
**Oxygen positional parameters for other carbonates are given in Table 2.
A
of the 0-0 distancE
within the C03 groups (2.22 K). In calcite, the shortest 0-0 distances between
and 2.93
A,
(2 x 1.36
0-0 distance~
in magnesite
are 2.85
which in many ways resembles
the other hand, it faithfully
=
tive ionic radius of oxygen
2.72 K). description,
The corresponding
respectively.
it does not strongly enough emphasize
larger than twice the effec-
Another
the description
disadvantage of corundum,
the rigid nature of the C0
represents
3
the proper orientations
of thi~ is that
group.
On
of the C0
3
groups, and leads to a correct choice of the unit cell. The formal description
of the calcite structure (and that of its isotypes) 2 The M + cation position is taken as the origin and is a
is given in Table 1. special position.
In addition
to being a center of symmetry, this site also As noted previously, the M2+ cation is 6-coordinated
lies on the triad axis. in the calcite structure, The dispositions 7.
forming a slightly distorted
of the octahedra
relative
Within a given layer, the octahedra
nor corners.
Adjacent
corners of octahedra
octahedra
octahedron
(Fig. 6).
to one another are shown in Figure
are independent,
sharing neither edges
are linked both by C0
groups and through the 3 (i.e., along the c axis).
from layers above and below
Each octahedron shares its corners with other octahedra,
three from layers above
and three from below. It is also useful to consider C03 group.
the coordination
Figure 8 shows such an arrangement.
sphere around an individual
Each oxygen is bonded to one
carbon and two cations, each of the latter from adjacent Both C and 0 lie on special positions,
as well.
symmetry 32 and the oxygen position point symmetry parameter which is not constrained
c-o
bonds are aligned parallel
2.
cation layers.
The C position has point The only positional
by symmetry is the x parameter
to the three a axes.
for O.
The
The overall point symmetry
for calcite is 321m. Calcite
isotypes
Charge balance
requires
that carbonate 8
isotypes of calcite contain only
Figure 6. Stereoscopic projection of a portion of the calcite structure showing the central Ca coordinated to six oxygens from distinct CO) groups, prepared using the program ORTEP (Johnson, 1965). Vibrational ellipsoids represent the 90% probability e Let ron distribution surfaces. Note the orientations of the oxygen ellipsoids.
Figure 7. Schematic projection down the a-axis showing one layer of Ca06 octahedra in calcite. Large closed circles are Ca atoms (not to scale) at the center of the octahedra. Open circles at corners of the octahedra are oxygen atoms; dashed lines of octahedra depict lower edges. Cj.osed and open circles between octahedra are C atoms in the upper and lower CO) layers, respectively. CO) groups link corners of neighboring Ca06 octahedra, as shown at left. Octahedra also share corners with other octahedra from layers above and below. The dotted triangle at top shows the basal edges of a Ca06 octahedron from the next layer above.
Figure 8. Stereoscopic projection of the coordination environment of a CO) group in calcite, prepared using the program ORTEP (Johnson, 1965). Vibrational ellipsoids represent 90% probability electron distribution surfaces. Note that the Ca and C ellipsoids are nearly isotropic, while that for oxygen is anisotropic.
9
divalent cations as major elements. to form calcite-type
carbonates
For at least two multivalent
(Mn and Fe), various
shown them to exist in the divalent Wildeman,
spectroscopic
state (e.g., Takashima
1970; Urch and Wood, 1978).
divalent cations:
Pistorius
the synthesis at high pressure
studies have
and Ohashi,
The calcite structure
bonates of the following (1960) reports
cations known
1968;
is found for car-
Ca, Mg, Fe, Cd, Mn, Zn, Co, and Ni. of a phase that might
be CuC0 , although confirmation is lacking. 3 Recent x-ray structure refinements have been done for calcite, magnesite, siderite,
otavite, rhodochrosite,
magnesian
calcite and a Cd-rich calcite.
most recent or complete
smithsonite,
and two solid solutions -- a
Selected structural
studies are presented
in Table 2.
some insight into the changes produced by substituting
data from the
These data provide
different
cations in the
structure. In order to understand
Atomic thermaZ vibrations. atom in its local environment, of their vibrational this description,
factors reported by Effenberger
3.
equivaZent
Ellipsoids
axis.
For
of the principal
axes
et al. (1981) for calcite, magAlong with these amplitudes,
isotropic temperature factors
of revolution,
the shapes and sizes
from the refined anisotropic
and smithsonite.
for the M2+ and C positions
to be ellipsoids
of an
as deduced from the thermal parameters.
ellipsoids were calculated
nesite, siderite, rhodochrosite, calculated
it is useful to consider
the root mean square (RMS) amplitudes
of the vibrational temperature
ellipsoids
the behavior
(B) are also given in Table
are constrained
the revolution
by point symmetry
axis coinciding with the 3-fold
For 0, which lies on a diad axis, the ellipsoid
is only constrained
to
axis coincident with the diad (i.e., the c-o bond direction) The amplitudes for M2+ and C in the R3c carbonates listed in Table 3 indi-
have one principal
cate that these ellipsoids hand, the ellipsoids coincides with the the
c-o
are nearly spherical
for oxygen are clearly anisotropic.
c-o
bond direction.
bond is by far the strongest
inclined with respect
shapes of the ellipsoids
The shortest axis'
This result is to be expected
in the structure.
in Fig. 8).
The ratio of amplitudes
Not surprisingly,
since
The longest axis is
in other respects as well.
This is especially
Calcite
isotropic
is somewhat anomalous
temperature
factors
larger than for the other pure carbonates,
pronounced
of this
for the longest to shortest axes is roughly
The equivalent
for calcite are considerably
the direction
to the "plane" of the 3-fold coordination
1.4 to 1.5, except in calcite where it is 1.9.
atoms.
On the other
to the c axis at angles varying from 22° to 480 (see the
longest axis is roughly perpendicular of oxygen.
in all cases.
(B) for all
for 0 where the B value for calcite is
twice that of the other pure carbonates. 10
These values reported
(for calcite)
,...., 00
a>
,....,
..... '-'
....;
....;
I-t
bI) .....
.... 4)
.....
,....;
4)
I-t .....
I-t
4) '-' bI)
4)
I-t '"
I-t
'"a>
....OS I-t
t.:>
a>
a> "I
,....,
-e- ,-,
'-'
00 0
"I "I
'-' 00 '-'
-o
N '-' 0 00 "I
"I'"
.....
,....,
'"
-o
'-'
00 r-,
oJ)
,-,,-, '-' ..... N 00 '-' '-' a>a>N
,-,
-e
00 '-'
a>
'" '"
'-' 0
... ...'" 00 0
a>
'"
"I
,-,
~
,-, N '-'
'" '"'" '" '" '" .....
oJ)
'-' r-, 0
'" '" '"
..... .....
...... .....
'-' 0 0
.....
.....
,-, "I '-' 00 00 N
N N
N
"I
N
"I
,...., ..... ,-,
,-,
8 .....
,....,
,-,
"I
1.1")
-o
NN
.....
oJ)
00
oJ)
a>
.....
.....
"I
'-' N N "I
,-, "I '-'
'-'
"I
00
oJ)
.....
N '-'
a>
'-'
oJ)
....
..... .....
'-'
'-'
-o
,-,
,....,
,-,
-o
r-, '-'
"I '-'
'-'
a>
00
.....
.....
'"
""
"" r-, "I
-o
-o
'"
"I
'"'" r-,
oJ)
N "I
N
"I
N
I-t
....
000
00
0
0
0
0
0
0
...
,....,
,-,
~ .....
;;;-
'-'
'-'
>
r-,
,....,
'" '-'
N '" ...."I 00 U":
oJ)
.......... .....
..........
,...., ,-,
,-,
00
a>
OJ
::0
4)
N
oJ)
r-,
N N '-' r-,
c2 '-' "'I
ell
N a> ,-, '-' ._, N
'" '" a> a>
'-' 00 "" 00 00
,-,
oJ)
..... 00 N
N 00
-o
""
00
"I 0
00
a>
.....
-o
..... '"
.....
oJ)
-o
,-, r-, '-'
,-,
a> a> a> """""
""""
.....
'"
-e-
z
oJ)
'-'
-o
1.1")
'-'
z
,-,
.....
N ,-, '-' 00 '-' N r-,
.....
I-t
0
'-'
.....
oJ)
4)
I-t
0
,....,
'" "" '" -o'" a>
N
.....
oJ)
-o
,a
,-, N '-'
.....
Vl
ell N
I" Calcite + Dolomite
5001-
-
>I
o
I
I
I
5
10
15
Figure 4. A portion of the calcite limb of the calcite-dolomite so Lvus . The reversal brackets and the solid curve are from the (unpublished) data of Fanelli and Wyllie (indicated as "This St udy" in the figure), using electron microprobe analyses of crystals grown 1n the presence of a liquid phase (see text). The dashed curve is the po!ybaric so!vus of Goldsmith and Newton (1969, see Fig. 3), and the dot-dashed curve from Goldsmith and Heard (1961).
Weight % MgC03 the dolomite
limb of the solvus is further complicated
order on lattice parameters tle under any circumstances.
by the effect of dis-
as well as by the fact that it changes rather litHarker and Tuttle
(1955) list a value of the
dolomite limb at 900°C as 43 wt % MgC03, or 47 mol %, the same as the Ca53Mg47 by Goldsmith and Heard (1961). At 500°C, Harker and Tuttle
determination
found 45 wt % MgC0
in the dolomite (their Sample 15), or 49.6 Mol %, and 3 and Heard report Mg . . Little has been done on the dolomite limb 49 5 since these studies. The Mg-rich dolomite limb and the magnesite limb in
Goldsmith
equilibrium
with it are steep and little affected by temperature
Consideration
of the magnesite-rich
at crustal temperatures
up to 900°C.
portion of the system, of little interest
and pressures,
will be considered
shortly with rela-
tion to studies under upper mantle conditions. Fanelli and Wyllie completed
(in preparation;
a study at 2 kbar of subsolidus
see also Fanelli
et al., 1983) have
and melting relations
in the system
CaO-MgO-C0 -H 0, and have re-examined the calcite limb of the solvus using 2 2 electron microprobe analyses. At temperatures of 650°C and above, the calcite and dolomite are in equilibrium crystals
grow to 25-30 µm.
for microprobe
analysis.
enough to analyze, reversed
with a hydrous carbonate
The dolomite and magnesite
melt, and the calcite
crystals are too small
Below 650°C the calcite crystals
although the system is subsolidus.
at 600°, 650°, 700°, and 750°C.
The equiiibrium
was
The Fanelli and Wyllie data are
shown in Figure 4, with the curves of Goldsmith 54
are still large
and Heard
(1961) and Goldsmith
and Newton Metz
(1969).
Earlier determinations,
(1976) investigated
discussed
above, are omitted.
tremolite + dolomite ~ foster site
the reaction
+ calcite + CO2 + HZO, and found the MgC03 content of the magnesian calcites produced
to be within 0.5 mol % of the solvus data of Goldsmith
(1961) and Goldsmith Puhan
and Newton
and Heard
(1969); see also Gordon and Greenwood
(1970).
(1978) determined
the MgC03 content of calcites produced by the reaction dolomite + K-feldspar + H20 ~ phlogopite + calcite + CO in the temperature 2 range 4l0o-640°C and found them in good agreement with the Goldsmith and Newton (1969) solvus. It would appear from the conformity techniques
that the calcite limb of the solvus is reasonably
the metamorphic temperature
temperature
range from greenschist
data would be desirable,
sitions is healthy,
but considering
and ease of exsolution in the carbonates
facies.
Lower
and further testing of equilibrium
compo-
the relatively
responsive
kinetic behavior
amount of back-reaction
rocks is to be expected
and is observed
Unless one can be sure that dolomite ex solved during retro-
gression can be distinguished
from that present at the "equilibrium
ture", and that it can also be
analyzed
tempera-
still 3 in solid solution in the calcite, little more than a "minimum" meta-
morphic temperature greater
well known in
to granulite
in this system, a significant
of metamorphic
(Goldsmith, 1960).
present
of these data obtained by different
can be determined.
(Gittins, 1979).
In addition,
along with the residual MgC0
The problem
in carbonatites
is even
the effect of other components
such
as FeC03 and MnC03 is not adequately known. Thus, for the purposes of geothermometry, further refinement of the binary CaC0 -MgC0 solvus appears 3 3 superfluous.
Relations at higher pressures and temperatures. melting and decarbonation
reactions
complicate
above studies moderate pressure was adequate In considering upper mantle, cifically
the Ca-Mg carbonates decarbonation
treated.
At higher tempeatures
the phase relations;
to maintain
under conditions
carbonate
in the solids.
more appropriate
to the
behavior will be indicated, but will not be spe-
Little will be said about melting, beyond indicating
on the CaC0 -MgC0 join. 3 3 Byrnes and Wyllie (1981) investigated
the subsolidus
it
and melting rela-
tions for the join CaC0 -MgC0 at 10 kbar, and Irving and Wyllie (1975) at 3 3 30 kbar, later corrected by Byrnes and Wyllie (1981) to 27 kbar. In addition, Irving and Wyllie deduced the relations on their pressure schematic
correction,
isobaric
calcite-dolomite
at 5, 6, 12, 15 and 25 kbar (or based
at 10% less than these values),
diagrams at these pressures.
and presented
The representation
of the
solvus and its behavior with pressure was taken from 55
Goldsmith
and Heard
(1961) and Goldsmith
and Newton
tion of fields in the diagrams not directly deduced from P-T data on decarbonation and Wyllie,
1975; Goldsmith
(1969), and the configura-
determined
experimentally
were
and melting of MgC03 and CaC03 (Irving decarbonation
and Heard, 1961), of dolomite
(Goldsmith and Heard, 1961), and P-T-X relations with respect to the calcite-aragonite
(Goldsmith and Newton,
1969)
transition
in the system CaC03-MgC03. Figure 5 shows the system aL 27 kbar, at which pressure no decarbonation takes
place, and the join is binary.
The aragonite-magnesian
tions and the lower temperature
portion
extrapolated
from Goldsmith
and Newton
calcite-dolomite
of the dolomite-magnesite
rela-
solvus,
(1969) are also illustrated.
Figure 6 shows the system at 10 kbar, only partially binary because of the presence
of peric1ase
(MgO) and vapor
of periclase
+ liquid + vapor, dolomite-like is included
for comparison.
The schematic
6, 12, 15 and 25 kbar from Irving and Wyllie The derivation
involving reactions
tailed here, but left for the aficionado 1975, especially
Fig. 6A).
+ vapor,
+ vapor.
isobaric
The 27
sections at
(1975) are shown as Figure 7 A-D.
of these diagrams from P-T data, extrapolations,
mated considerations
Wyllie,
in ternary fields
carbonate + periclase
carbonate + periclase
and a small field of magnesite-like kbar diagram
(C02) represented
and some esti-
in the join CaC03-MgC03 is not deto pursue on his own (see Irving and
Extrapolation
of the "dolomite"-magnesite
solvus at 27 kbar into the melting interval of Figure 6 gives a temperature approximately
l410°C for the solvus crest, still metastable
At somewhat higher pressures
the melting
of
at this pressure.
interval consists of a simple loop
with a minimum on the liquidus. In Figure 7 B-D the encroachment the calcite-dolomite of the Mg-free between
of aragonite
solvus is apparent.
aragonite
(plus Mg-calcite)
it and the single-phase
At still higher pressures continues
field of Mg-calcite
reaches the crest of the solvus, as indicated variant point where aragonite, It should be emphasized
on the Mg-calcite
Mg-calcite,
that the diagrams
limb of the field
to grow until the boundar: at higher temperatures
in Figure 8, producing
an in-
and dolomite are in equilibrium. of Figures
7 and 8 are largely
deduced and not known in detail. Nothing reactions
substantive
of the various
MgC03 at relatively Byrnes and Wyllie, fining pressures
has been said about the very important decarbonation carbonates.
high pressures
1981), all other investigations
that exceeded P
tions would significantly ena, and equilibria
With the exception
and temperatures
'
of the system CaC0 3 1975;
(Irving and Wyllie,
were carried out at con-
To discuss the known decarbonation
relaC02 lengthen this review, and along with melting phenom-
in hydrous systems, is beyond the scope of this paper, and 56
1500
u
0
~ ~
1000
C1>
a. E
~
500,
Ar+Cd
Cd+Cm
5 kb Ar+Cd
00
20 40 60 80 1000 20 40 60 80 100
CaC03 Figure
6 (to
the
join at 10 khar.
Mole % MgC03 right).
Figure 5 (to the left). On the. left is the isobaric temperature-composition section of the CaCOrMgC03 join at 30 kbar (later corrected to 27 khar) , in part extrapolated from data of Goldsmith and Newton (1969). Cc, Cd and em refer to carbonate solid solutions related to calcite, dolomite, and magnesite, respectively, at lower pressures and temperatures.. On the right is the section at 5 kbar. From Irving and Wyllie (1975, Figs. 6B and 6C).
MgC03
The CaCO MgC0
r
3
Salvus curves from Gold-
smith and Heard (1961). Also shown are results of Irving and Wyllie (1975) at 30 kbar, subsequently recalibrated to 27 kbar. Cc:: c a Lcd t e solid solution. em = magnesite
solid solution, Do - dolomite solid solution, Cd - carbonate solid Bolution near dolomite composition, Pe - periclase, L_ liquid, Wyllie
V - CO2 vapor. (1981).
From Byrnes
and
Figure 7 (below). Schematic isobaric sections of the join CaC03-MgC03 (see Irving and Wyllie, 1975, for details of construction). The isobars show successive changes as pressure increases from 5 kba r (Fig. 7D), to 30 kbar (corrected to 27 kbar , Fig. 5, left-hand diagram).
CoC°3 V
Ferroon Calcite Solid Solution
Zn
Fe
>
>
Co
>
Ni »
Cu.
doubt as to the stability of Zn-dolomite,
it falls
higher in their series than does Fe, and may therefore be considered being a contender Garavelli CaZn(C03)2
et al. (1982) described
from Tsumeb, Namibia,
minrecordite.
close to
for dolomitic honors. the first occurrence
associated with dioptase,
It shows evidence of cation ordering
of a nearly pure that they named
consistent with the
space group, and is also associated with an impure, magnesian well as a garden variety
of zincian dolomite
R3
variety, as
in several dioptase druses.
The
rarity of CaZn(C03)2 argues against a large stability field, but the existence of an ordered compound also argues against a crystallization as a metastable compound;
metastable
or configurationally Minrecordite "second oxidation
crystallizations
tions is presented
is questionable
it was formed in the
evidence of instability,
in Figure 15.
representation
The temperature
phases might be rather low.
amount of the natural material
A note on the asymmetry
but it is
is a compound with a maximum temperature
and highly conjectural
tion to two disordered obtain an adequate
at a low temperature;
The fact that it was not formed by reaction of the
that Zn-dolomite
A schematic
disordered
zone" (Garavelli et a L, , 1982), along with dioptase, a hy-
end members at 600-750°C
ence.
of high-entropy,
simple forms.
crystallized
drous copper silicate.
possible
are generally
of exist-
of its phase rela-
of the suggested decomposiIt would be desirable for experimental
to
study.
of the solvi
All of the solvi under consideration er amount of solid solution
is observed 65
are asymmetric,
such that the great-
in the limb representing
the larger
cation.
This phenomenon
is not restricted
tional solid solution it is generally
to carbonates,
the larger one with greater ease than vice versa. observed
in the reaction
mechanism
smith and Graf, 1960).
for in a substitu-
true that the smaller ion can replace This behavior
can also be
of, for example, MnC0
At low temperatures
with MgC0 (Gold3 3 when reaction is incomplete, it
was observed
that the MnC03 has taken some MgC0 into solid solution, leaving 3 pure MgC03 unreacted. This disequilibrium example of Mg-rich compositions reacting less completely than the Mn-rich ones is analogous to
essentially
the strain-energy
control of the equilibrium
solvi with asymmetrical
limbs.
TERNARY PHASE RELATIONS The combinations of CaC03 and MgG03 with FeC0 , MnC0 , CoC0 , and NiC0 3 3 3 3 are the only ternary systems to be experimentally investigated to date. It will become apparent that additional systems
(CaC03-MgC03-FeC03)
work is needed, and only one of the four
has even been considered by a second laboratory.
CaC03-MgC0 -FeC03 3 This system has been examined by Rosenberg et al. (1962).
Rosenberg
sels with samples in gold-foil carbonate
solution to promote
largely between
2-3 kbar.
(1960, 1967), and by Goldsmith
worked from 350° to 550°C in cold-seal pressure vesenvelopes
(containing a drop of O.OlM alkali
+ ~ 2% CO atmosphere 2 et al. (1962) produced isothermal sec-
reaction)
Goldsmith
open to a CO
tions at 600°, 650°, 700°, 750°, and 800°C, for the most part at 15 kbar, in an opposed-anvil
device.
Figures
16 and 17 contain the data of Rosenberg
(1967) and Figures 18 and 19 those of Goldsmith The two sets of data have no overlapping general configuration
of the diagrams
aries are significantly
different.
phase triangle containing
et al. (1962) at 600° and 650°C.
temperature
range, and although
is the same, the locations
the
of the bound-
At 550°C the ankerite corner of the three-
a calcite-rich,
a siderite-rich,
and an Fe-rich dolo-
determination is (mol %) FeC0 = 36, MgC0 3 3 9, CaC03 = 55. Goldsmith et al. at 600°C show FeC0 = 21, MgC0 = 27, CaC0 3 3 3 = 52. Rosenberg's data show rather small changes with temperature. At 450°, mite (ankerite) in Rosenberg's
the temperature where most of the work was done, the ankerite
corner is at
= 33, MgC03 = 13, and CaC03 = 55. Goldsmith et al. show a larger shift, in only 50° to 650° to FeC03 = 27, MgC03 = 21, CaC0 = 52. Both data sets 3 indicate that CaFe(C03)2 is not stable under these conditions, but Rosenberg
FeC03
shows significantly
more Fe-substitution
three-phase
The single~phase
field.
field of dolomite-ferroan
ite in both studies lies on the Ca-rich and natural ankerites
in ankerite along with a narrower
side of the CaMg(C03)2-CaFe(C03)2
also show excess CaC0 . 3 66
dolomite-ankerjoin,
Figure 16 (left). Subsolidus r lations in the system CaCOrMgCOrFeC03 at 450 C. D dolomite solid solution, C = calcite solid solution, S :::; siderite-magnesite solid solution. Open circles, one-phase; filled circles, two-phase; and triangles, three-phase assemblages. From Rosenberg (1967. Fig. 1).
5
=
Figure 17 (below). Three-phase triangles in the system CaCO)-MgC03-FeC03 for temperatures of 4000C, 4500, (shaded) and SOOoC shown superimposed. From Rosenberg (1967, Fig. 4).
/
,I
CaC03
It is unlikely attributed
that the sizeable differences
to the difference
calcite and magnesite
in pressure.
in the two studies can be
The sum of the molar volumes of
is very little larger than that of dolomite,
sure has very little effect on the stabilization molar volumes of ankerites
of dolomite.
to reconcile
and pres-
Although
the
are not known, it is also likely that pressure
would have rather little influence on solid-solubility difficult
I
the differences
relations.
It is also
on the basis of the temperatures
of
the studies. I see no basis for selecting as being closer to the truth. mental data base is clearly boundaries
Figures
Either or both can be in error.
inadequate,
in modern apparatus
temperatures,
one over the other of these investigations
is essential
to assure equilibrium.
20 and 21, the single-phase
composition
of dolomite,
composition
CaFe(C03)2'
CaMg(C03)2'
The experi-
and, at least some reversals
field originating
of phase At higher at the
extends as a thin sliver toward the
curving toward and enlarging 67
into the CaC03 apex
CoCO. Figure
The system CaCOrMgC03-FeC03 at 600oC,
18.
under a confining pressure of 15 khar. The solid solubilities shown in Figures 20-24 for the binary join CaCO)-MgC03 are taken from Goldsmith
and Heard (1961). from cles
Those in the join
CaCOrFeC03
the smoothed curve of Figure 15. Open cirindicate single phases, filled circles, two-
phase assemblages. Fig. 5).
From Goldsmith et al.
(1962,
CoMg(CO.),
MgCO.
FeCO.
CoCO. Figure under
19.
The system CaCOrMgCOrFeC03 at 650°C,
confining
in Figure
pressure
18.
of
15 kbar.
From Goldsmith e t al.
Symbols
as,
(1962, Fig. 4).
CoMg(CO.),
----MgCO.
after traversing Goldsmith temperature
approximately
that have Fe-contents
(1978) states
of the distance.
and suggested
The tendency
diagenetic
equivalent
of natural
ankerites
Matsumoto
metastability
(1978) and Matsumoto
from coal fields in Japan
to those of the ordered compounds
et al. (1962) at temperatures (p. 355), "It is noteworthy
68
low-
that some of them may
for compositional
has already been noted.
(1981) describe
by Goldsmith
ankerites,
compositions.
in several carbonates and Iijima
two-thirds
et al. (1962) noted the high Fe-contents
(sedimentary)
have metastable
FeCO.
of 600°C and above. that the carbonates
produced
Matsumoto contained
in
CoCO. Figure 20. The system CaC03-MgCOrFeC03at 700oC, under confining pressure of 15 kbar. Open circles indicate single phases, filled circles, twophase assemblages. From Goldsmith et a L, (1962 Fig. 3). I
----Mgco.
FeCO. CoCO,
Figure under
21.
The system CaCOrMgCOrFeC03 at 800°C,
a confining
as in Figure Fig. 1).
pressure
20.
of
15 kba r .
Symbols
From Goldsmith et a1.
(1962,
MgCO,
clastic
sediments
of chemical
FeCO,
of the coalfield
composition
as shown in Figure 11, compared with synthetic car-
bonates at higher temperature Rosenberg
(1967)."
Although
an4 pressure
given that the equilibrium
thermometer.
et al. (1962) and
in the investigations
of Gold-
(1967) make for real uncertainties,
Fe-content
is completely
makes the use of the Fe-content as a geologic
by Goldsmith
the differences
smith et a1. (1962) and Rosenberg
low temperatures,
regions studied provide much wider ranges
of ankerite,
unknown,
in ankerites
At higher
at rather
of metastability
and ferroan dolomites
(metamorphic) 69
particularly
the possibility
and
temperatures,
suspect where
equilibrium
might be more likely, it would be desirable
compositions
against an independent
to check ankerite
geothermometer.
CaC03-MgC03-MnC03 This system was investigated
at 500°, 600°, 700°, and 800°C by Goldsmith
and Graf (1960) in an opposed-anvil
device at 10 kbar.
trate the system at 500°, 600°, and 800°.
Figures 22-24 illus-
At 500° the presence of a solvus
between CaMn(C03)2 and MnC03 is shown in'Figure 22; at the higher temperatures solid-solubility between CaC03 and MnC03 is complete. The diagrams, particularly the size and shape of the three-phase
area, illustrate
greater solid
solubility
in general than in the system CaC03-MgC03-FeC03• The join CaMg (C03)2-CaMn(C03)2 is binary only at temperatures above approximately 700°C,
probably a result of the fact that Mn enters the Ca as well as the Mg position of the dolomite
structure,
producing
the case of Fe substitution Order-disorder
relations
a Ca-deficient
where ankerites
ordered compound,
unlike
show excess Ca.
in Fe- and Mn-containing
dolomites
In the system CaC03-MgC03-FeC03, at temperatures below approximately 675-700°C the ankerite corner of the three-phase triangle (Figs. 16-19) marks the limit of Fe solubility, At the higher temperatures
represented of Figures
by an ordered dolomite-type 20 and 21 the equilibrium
structure.
degree of
order of the ferroan dolomites within the single phase field originating the composition
of CaMg(C03)2 Figure 25 is a representation
is a function of temperature
of the limits of order as observed by the pres-
ence of several of the dolomite ordering reflections matter is discussed probable
in some detail by Goldsmith
at 700° and 800°C.
This
et al. (1962), and it is
that some degree of cation order extends beyond the temperature
compositional
region in which ordering reflections
powder diffraction
at 500°C and 800°C. in x-ray scattering
the compositional
factor produced by the substitution
Furthermore,
corner of the three-phase
of Mn for Mg makes
in x-ray powder diffraction
photographs
limits of detectable
more
order are even
Mn enters the Ca as well as the Mg-site, adding a
degree of freedom, which enhances disorder.
a better indication
region in which cation order
in the system CaC0 -MgC03-MnC0 can be detected 3 3 As discussed by Goldsmith and Graf (1960), the increase
so in this system the observed
more suspect.
are detectable with x-ray
structure)
detection of order reflections difficult,
and
techniques.
Figure 26 illustrates (the dolomite-type
at
and composition.
It may well be that the upper
triangle at the several temperatures
of the limits of cation order.
70
studied may be
Figure 22. Subsolidus relations in the system CaC03-MgC03-MnC03 at 500·C and 10 kbar total pressure. Filled circles indicate reaction products that are single phases; open circles, twophase; diamonds, three-phase assemblages. Tie lines are shown in the two-phase areas. The join CaMg(C0 ) 2-CaMn(CO ) 2 is indicated by a dotted 3 line. An additional inferred ,two-phase region is indicated by the dashed line. From Goldsmith and Graf (1960, Fig. 1).
Figure 23. Subsolidus relations in the system CaCOrMgCOrMnC03 at 600·C and 10 kbar total pressure. Symbols and tie lines as in Figure 22. The join CaMg(C03)2-CaMn(C03)2 is indicated by the dashed line. From Goldsmith and Graf (1960, Fig. 2).
Figure 24. Subsolidus relations in the system CaCOrMgCOrMnC03 at 600·C and 10 kbar total pressure. Symbols and tie lines as in Figure 22. The join CaMg(C03)2-CaMn(C03)2 is indicated by a dotted line. The position of the threephase triangle at 800°C was determined from only two runs, and the dashed line indicates somewhat greater uncertainty in its position than at lower temperatures. The inferred two-phase region along the base of the three-phase triangle is also indicated. From Goldsmith and Graf (1960, Fig. 4)
._. __
_.-..CoMnco,',
," ,
,'j
'0'
f ..:
,/'
71
700'C {IO·I}
visible
{OI'5}
and
{OO'3}
visible
from P 10 Q
{02"}
visible
from
from
P to 5
R to T
800'C
Figure
{IO.'}
visible
{OI'5}
ond{02.t}
from P'io
{OO'3}
visible
Q'
visible
from
R'
from
p'to
S'
T'
to
Compositional regions in the system CaC03-MgC03-FeC03 at (a) 70Qoe, and the several ferroan dolomite ordering reflections are visible in powder X-ray diffraction films. These two diagrams are enlarged central portions of Figures 22 and 24 to which letters have been added. In determining the positions of the letters, the presence or absence of the ordering reflections was noted in X-ray film of products from the runs shown in the figures. Inferred tie lines through the experimental points were used to locate the ferroan dolomite compositions on the upper and lower boundary curves of the single-phase region. From Goldsmith et a1. (1962, Fig. 8).
(b)
25.
BOOoe in which
\
eeo-c Figure 26. The compositional regions in the sys.tem CaC03-MgC03-MnC03 the dolomite-type structure can be observed in powder X-ray diffraction The grid of dashed lines gives compositions at intervals of 5 mol %. (1960, Fig. 7).
The systems CaC0 -MgC0 -CoC03 3 3
and petrology.
Their investigation
shed on the nature of divalent bility of the dolomite forming cations.
at 500° and 800°C, in which diagrams, are stippled. From Goldsmith and Graf
and CaC0 -MgC0 -NiC0 3 3 3
Neither of these systems plays any significant mineralogy
MnC03
was undertaken
cation substitutions
structure
Opposed-anvil
in the presence apparatus
deal of difficulty with decomposition
role in the real world of for the light
in dolomite and the sta-
of the various carbonate-
was used for both systems.
of NiC0 - and CoC0 -rich 3 3
A great
mixtures was
encountered. This system was investigated and 750°C at a confining pressure 0
tem at 600
0
and 750
of 15 kbar.
and are not reproduced
0
here.
The resemblance 72
650
0
,
Figure 27 illustrates
the 650 and 700°C diagrams are intermediate 0
;
at 600
,
700
0
,
the sys-
in appearance
to the system CaC0 -MgC0 -FeC0 3 3 3
CoCO,
CoMg(CO')2
MgCO, CoCO, Figure 27. The system CaC03-MgC03-CoC03 (a) at 600°C and (b) at 750°C under confining pressure of 15 kbar. Open circles indicate reaction prod':" ucts that are single phases; filled circles, two phases; triangles, three phases. The join CaMg(C03)2-CaCo(C03)2 is indicated by the light broken line. Fields that are inferred or not well delineated by experimental runs are indicated by broken lines. From Goldsmith and Northrop (1965, Figs. 1 and 4). CaMg(CO,l,
MgCO,
at temperatures
CoCO,
below 6750 is apparent.
At 600°C the field of cobaltoan
dolo-
mite extends approximately 22% toward the hypothetical CaCo(C0 )2; approxi3 mately 11 mol % Mg2+ is replaced by Co2+. At 750°C the upper limit of substitution of Co2+ in dolomite is approximately 26%. The ternary relations
in this system are more com-
plex than in those of CaC03 and MgC03 with MnC03, FeC03, and CoC0 . The mis3 cibility gap between magnesite and NiC0 produces an additional three-phase 3 triangle. The system was studied at 6000, 7000, and 7500, and Figures 28a and 28b are the results
at 600° and 750°C.
In Figure
28a the fields labelled
I-XI are as follows: Single-phase I
Calcite
fields: containing
Ni2+ and Mg2+ in solid solution 73
CoCO, I
a
600 C D
Figure 28. The system CaC03-MgC03-NiC03 (a) at 600°C and (b) at 750°C under confining pressure of 15 kbar. Open circles indicate reaction products that are single phases; filled circles, two phases; triangles, three phases. See text for discussion of the two three-phase triangles and for identification of fields. The join CaMg(C03)2 -CaNi (C03) 2 is indicated by the light broken line. Fields that are inferred or not well delineated by experimental runs are indicated by broken lines. From Goldsmith and Northrop (1965, Figs. 6 and 8).
b
7S0 C D
CoMg(CO,),
II III
Nickeloan dolomite 2+ 2+ Magnesite containing Ni and some Ca in solid solution IV Nickel carbonate containing Mg2+ and Ca2+ in solid solution Two-phase fields: V
VI VII VIII IX
Coexisting Coexisting Coexisting Coexisting Coexisting
Three-phase X
XI
calcitic solid solutions and nickeloan dolomites nickeloan dolomites and magnesite solid solutions magnesite solid solutions and NiC0 solid solutions calcitic solid solutions and NiC0 3 solid solutions 3 solutions nickeloan dolomites and NiC0 SOlld 3 triangles:
The compositions of the three coexisting phases are determined by the apices of the triangle: nickeloan dolomite, calcitic solid solution, and NiC03 solid solution The compositions of the three coexisting phases are determined by the apices of the triangle: nickeloan dolomite of a composition slightly different than that in X, magnesite solid solution, and NiC03 solution slightly different from that in X 74
of Ni2+ for Mg2+ in dolomite
The substitution between
600
0
dolomites
and 750
increases very little
in this range it is from 13 to 15 mol %.
0 ;
synthesized
in this and in the Co-containing
All of the
system appear to have
a high degree of cation order. SUGGESTIONS The disconcerting
differences
FOR FUTURE WORK
in the results of Rosenberg
smith et al. (1962) in the system CaC03-MgC03-FeC~3
(1967) and Gold-
require resolution;
equi-
librium reversals in modern apparatus are necessary to establish the extent of Fe2+ substitution in dolomite as a function of temperature, as well as the compositions three-phase
of the coexisting
triangle of Figures 16-19.
Of the ternary carbonate Mg has been independently
be desirable,
systems that have been investigated,
examined by more than one laboratory.
tion of the systems containing
verified
calcitic and sideritic phases making up the
on any carbonate
features be
system other than CaC0 -MgC0 . 3 3 with dolomite, because of its mineralogical
logical importance
would also
There has been rather little modern experimental
The preoccupation
sideration
Re-investiga-
Mn, Co, and Ni in modern apparatus
at least to the extent that their most important
or disproved.
only Ca-Fe-
is understandable.
of compositional
variants
work
and petro-
but lessons can be learned from the conof the dolomite-structure
type.
Kutna-
horite, CaMn(C03)2 is known as an ordered (R3) compound from several localities although it is a rather rare mineral. Although solid solutions along the join CaC03-MnC03 are readily synthesized (Goldsmith and Graf, 1957; de and Peters, 1981, and others), the ordered compound CaMn(C0 )2 has 3 not been produced, although the problem of detection of ordering reflections Capitani
in x-ray diffraction synthesis
of ordered structures,
low temperatures carbonates
powder patterns
particularly
has been considered
in Goldsmith,
has been mentioned.
of
those that are stable at rather
elsewhere
(see discussion
1959), and the onset of disorder
horite was observed at a temperature
The difficulty
as low as 450°C.
with respect to
in a natural kutna-
Thus, the crystalliza-
tion of ordered CaMn(C03)Z may at least in part be complicated by difficulties inherent in syntheses at low temperatures. Little consideration has been given to the possibility compounds;
of significant
a high degree of short-range
order would go undetected Ca-Mn carbonates
order in dolomite-like
order in the absence of long-range
by x-ray methods.
No structural
refinements
have been carried out, and other determinative
might be worthwhile. dolomites
short-range
Schindler and Ghose
with electron
paramagnetic
amounts of Mn, and although
(1970) have examined
resonance;
a preference 75
both contained
of
techniques two natural but trace
of Mn for the Mg site was apparent,
no work has been done on Mn-rich material.
Nuclear magnetic resonance tech-
niques on Ca-Mn compounds might also prove fruitful. The recent discovery of minrecordite (Zn-do1omite is a much more descriptive and palatable name) whets the appetite of the friends of the dolomite minerals.
Determination of the stability relations of CaZn(C03)2 would make at least several of these friends very happy, and might even be of interest to a larger segment of the mineralogical and geochemical population.
Synthe-
sis of Zn-dolomite has not been successful, but it has not been attempted at temperatures below 600°C, and lower temperature syntheses should be tried. If natural crystals are available, combined thermal (heating under elevated CO2 pressures) and single-crystal x-ray work could produce information on stability and/or order-disorder relations. It has been mentioned that additional thermodynamic information on carbonates is needed.
Data on solid solutions, as well as on ordered versus
disordered phases, is lacking.
For example, although it is known that mag-
nesian calcites and aragonite are metastable in sea-water with respect to essentially Mg-free calcite, the relations between the common Mg-calcites and aragonite are unknown.
At what magnesium concentration does calcite
become unstable with respect to aragonite?
The paucity of data is at least
in part due to calorimetric problems produced by the release of CO2 during Capobianco and Navrotsky (1983) have reported what
dissolution of carbonates.
appears to be the first successful work on carbonates.
The solvent was an
aqueous mixture of RCI and LiCl, and although it is not known whether or not the CO2 remains in solution (A. Navrotsky, pers. comm.), data are apparently reproducable. It is hoped that future work with this technique or perhaps with the use of a pressurized calorimeter will be carried out to produce the data badly needed to fully understand carbonate stability relations. Little attention has been given to thermal dissociation of carbonates. Good high temperature-high pressure data are not available for most of the carbonates, including many of the common minerals.
For example, calculation
of CO2 properties at high temperatures and pressures above 10 kbar relies on experimentally determined decarbonation reactions. These reactions involve magnesite and the accuracy of the calculation is strongly influenced by knowledge of the thermodynamic properties of magnesite. magnesite has not been accurately determined.
The Pc0 -T curve for 2 This and similar data on other
carbonates would provide better information for equation of state projections, adding to our knowledge of mantle geochemistry.
The inferred carbonates in
peridotite compositions are dolomite at lower pressures and magnesite at higher pressures.
ACKNOWLEDGMENTS
The author is indebted to R.C. Newton for the concept of Figure 12 and for helpful discussions, to David M. Jenkins for a variety of helpful acts, and to the National Science Foundation for Grant EAR 78-13675. 76
3
SOLID among
SOLUTIONS
METAMORPHIC
APPLICATIONS
and
SOL VI
CARBONATES
to GEOLOGIC
with
THERMOBAROMETRY
Eric J. Essene
INTRODUCTION There has been great interest ing carbonates experimental
in using the compositions
as geothermometers,
work of Goldsmith
due in large part to the extensive
and coworkers
(see Chapter Z for a discussion
of coexist-
on various
of the available
rhombohedral
carbonates).
petrologists
have directed most attention
carbonate
experimental
Of all the available
equilibria,
systems
data on
metamorphic
to the system CaC0 -CaMg(C0 )Z 3 3 in many marbles.
because of the common occurrence of calcite and dolomite The first applications powder diffraction
of calcite-dolomite
measurements
to estimate
despite the problem of retrograde and Heard, 1961).
exsolution
relied on X-ray
the MgC0
content of calcite
3 (Goldsmith,
1960; Goldsmith
With the advent of electron microprobe
followed a period of general disenchantment because of the recognition cite compositions applications
thermometry
of retrograde
to low temperatures.
of carbonate
thermometry
studies, there
with carbonate
resetting However,
thermometry
of many natural
the number of successful
has steadily mounted
ten years, and it is now clear that calcite-dolomite useful in contact and regional metamorphic
cal-
in the last
thermometry
rocks subjected
can be
to tempera-
tures between 400° and 650°C. In contrast
there have been few successful
able phase equilibria ates.
Despite
the availability
CaC03-MgC03-FeC03, estimates
in other carbonate
of metamorphic
with these systems
equilibria
temperatures
invariably
have been obtained petrologist themselves
or are these carbonate
and pressures?
These
below.
EXPERIMENTAL Of the many experimental
carbon-
in the systems
are the experiments
of equilibrium,
reset at low temperatures
questions will be discussed
of the avail-
few accurate
Has the metamorphic
these experiments,
representation
experiments
and CaC0 -srCo , 3 3 and/or pressures
(pace Barron, 1974).
been remiss in ignoring still an inadequate
of numerous
CaC03-MgC03-MnC03,
applications
systems to metamorphic
DATA BASE
determinations
of carbonate
only a few in the systems CaC03, CaC03-CaMg(C03)Z' 77
equilibria,
and CaC0 -FeC0 3 3
have
been tightly
reversed
(see Essene,
1982, for a discussion
of solvus
reversals).
The solvil in the systems CaC03-CaMg(C0 )2 and CaC0 -FeC0 3 3 3 as well as the calcite-aragonite transition in the system Caco have been 3 well reversed and appear to be accurately located equilibria for crustal metamorphites.
Many of the early experimenters
ment of both compositional
and structural
0
rapid at T > 500 C, although and Wyllie
(1982).
assumed
equilibrium
this has recently
that the attain-
was relatively
been questioned
Some of the early data were obtained
and related nonhydrostatic
experimental
reversed
data subsequently
obtained
cylinder
or rod bomb devices)
revisions
in the locations
crepancies
among different
devices,
although more carefully
in more hydrostatic
have generally
experiments
systems
necessitated
of the equilibria.
by Byrnes
in piston-anvil
However,
(piston-
only minor remaining
(e.g., see Anovitz
dis-
and Essene,
1983, on the system CaC03-MgC03-FeC03) suggest that the assumption of equilibrium in all experiments should be tested, ensuring careful reversals of appropriate
structural
by characterization
of run products with microprobe
electron
in addition
microscopy
Goldsmith provide
the experimental
Compositions
data relevant
by X-ray diffraction
1970), by wet-chemical
analysis
rocks have been obtained 1955; Goldsmith
1960; Sheppard
(Engel and Engel,
1970; Gittins,
1973; Puhan,
Michigan).
1976; Essene and coworkers
Powder x-ray by measuring
tional change
is relatively
in solid solution
(sub)microscopic intergrowths
allows
exsolution
1958; Carpenter,
analysis
(e.g., Hutcheon
at the University
estimation
or cell parameter
(Graf, 1961; Goldsmith
this technique
components
diffraction
a d-value
of carbonate
sensitive
et al., 1961; Bischoff
in calcite.
are formed in magnesian
of com-
to composiet al., 1983).
rapid, results are affected
(Goldsmith
et al.,
and Schwarcz,
1979), by atomic absorption
(Kretz, 1980) and by electron microprobe
and Moore,
positions
analysis
6
COMPOSITIONS
in metamorphic
1955; Goldsmith,
and Schwarcz,
techniques.
in Chapter
to this chapter.
(e.g., Graf and Goldsmith,
1955; Harker and Tuttle,
1967; Sheppard
5, and Carlson
OF CARBONATE
of carbonates
chemistry
and analytical
to standard x-ray diffraction
in Chapter 2, Speer in Chapter
DETERMINATION
While
states, as well as determining
by other
et al., 1961) and are plagued by Indeed if submicroscopic
calcites
then coherency
coherent
strain may
1 The term solvi will be used loosely in this paper for the miscibility gaps in carbonates of broadly similar struotures (e.g., rhombohedral) whether or not complete solid solution has been found at high enough temperatures. 78
shift the d-values
sufficiently
to yield incorrect
for even the calcite
lamellae.
absorption
analysis,
X-ray diffraction
analytical
technique
which disregards
possibility
of compositional
powder diffraction obtaining
analyst.
20 µm whenever
amperes
is followed.
Unfortu-
under the same conditions
and obtain poor results.
are best analyzed
Because
long wavelength
to 10-
is desired,
it is
less than 0.007 micro-
conditions.
due to differential poorly understood
heating factors.
The correction
by fixed stoichiometry
and other
the carbon
the
in the
to avoid erroneous
With due care and adequate analytical
standards,
totals
it is
(including
CO2) of 100 ± 2 wt %. analysis
by staining
the textural
examined
before preparing
and redistributes
Thallium
of coexisting
in thin section.
the polished
thin section.
Acid Phthalate,
RAP 79
Red S - dilute
Staining
the
flatness
in the calcite.
are common in magnesian
(1) zoning from magnesian
car-
This is often fa-
it alters the required
Mg and other minor elements
Two kinds of heterogeneities rocks:
relations
the bottom of the chip with an Alizarin
side should be avoided because
metamorphic
calculate
or fixed weight
to obtain acceptable
should be carefully
HCl mixture
by grain-size
program used for reducing
data should explicitly
Before beginning
cilitated
such as TAP or RAp2,
for Mg even under these
checks should be run on both
which is affected
microprobe
corrections.
of time
in the development
beam damage may vary from sample to sample
electron
stoichimometric
crystals
analyses
Volatilization
because
unknowns
possible
of recent advances
excellent
for the
at 10 or 12 kV instead of
(typically
spectrometer
to obtain
and unknown
atomic number
used
Volatilization
beam should be opened
If a 1-2 µm spot analysis
to use low currents
10-20 seconds).
restrictive
polished
is now a quantitative
practice
and the electron
possible.
it is now possible
bonates
tool for systems.
sample current on brass) and to count for short periods
of sensitive
usually
and ignores the
and some synthetic
of carbonates
carbonates
silicates
voltage,
important
(typically
standard
relations
is a bulk
under the electron beam can be a serious problem Carbonates
15 kV operating
especially
in natural
analysis
analyze
for the more refractory
unwary
textural
and atomic
practiced
For these and other reasons, x-pay
tool if proper analytical
some operators
of the carbonate
like wet chemical
as routinely
zoning.
compositions
microprobe
and accurate nately
compositions
should not be used as the primary analytical
carbonate
Electron
In addition,
inferred
calcites
cores to calcian
Rubidium
from
rims, and
Acid Phthalate.
(2) microscopic is presumably
exsolution regulated
of dolomite.
by diffusion
other cases the distribution to interpret.
analyze
closest
calcites.
cores of the larger to peak metamorphic
1982; Wada and Suzuki,
1983).
calcites
ter (1967), and Nesbitt
calcite
are present
the rims deficient Perkins
dolomite
stepping
annealed
calcite-dolomite excess dolomite 1967; Valley calcites
granules
into a granular
avoiding
1973; Puhan,
Exsolution
1976;
lamellae
assemblage
and Essene,
in dolomite-rich
The released
of interstitial
dolomite
texture resembling
1980).
buffered
by
1960; Carpenter,
It is safer to apply thermometry
marbles
throughout
(Goldsmith,
which
a high-temperature
but which was not necessarily
COMPOSITIONS The compositions
low temperatures
et al., 1979).
at the peak of metamorphism
with excess dolomite
within
exsolution
by step analysis
or else anomalously
(Puhan, 1976; Perkins
often forms external
may become
et al. (1982) all
If microscopic
1983).
in
(1960), Carpen-
have often been lost to the host and these areas
during
will be obtained
(1979) and Perkins
and Essene,
and Essene,
of dolomite
Goldsmith
(Hutcheon and Moore,
et al., 1982; Treiman
near grain boundaries must be avoided
exsolution
they must be reintegrated
in dolomite
the
(Sobol and Essene,
1982; Nesbitt
of this feature.
and
one should
grains to obtain
conditions
Microscopic
and Essene
but in
profiles
For zoned calcites
has long been known;
have shown photomicrographs lamellae
during exsolution,
and
is more erratic and difficult
1973; Brown et al., 1978; Bowman and Essene,
former magnesian
is often regular
(1983) show some excellent
in metamorphic
the magnesian
temperatures
of Mg/Ca
of magnesium
Wada and Suzuki
maps of magnesium
The zoning
which must have remained
to
saturated
metamorphism.
OF METAMORPHIC
of most metamorphic
CARBONATES
carbonates
are well represented
the tetrahedron
are usually coexisting
CaC03-MgC03-FeC03-MnC0 . Carbonates from marbles 3 close to the CaC03-CaMg(C03)2 binary, and one often finds calcite and dolomite. Carbonates in carbonated ultramafics
and some iron-formations no miscibility
lie along the MgCo -FeC0 binary, and because 3 3 gap is found along this join, only one carbonate phase is
found in this portion of carbonate many metamorphosed
manganese
1981) while others
locus of a solvus between
space.
The carbonates
deposits
some showing no compositional Peters,
composition
of
lie close to the CaC0 -MnC0 join, 3 3 gaps (Winter et al., 1981; de Capitani and
show a gap consistent rhodochrosite
with the experimental
and kutnahorite
(Goldsmith
and
DC
__
.....
.~- . ..
600l
-
500f
B
. - .........
"at
I
Am M
,... . ... .
I
I
I
• .....
.
••••
lA
4 ....
.•"--.'15
I
50
CoCO:l Figure MnC03' tures. tirama 1980).
....
,M ••
(Mn.Mg.r.lCo,
Mole %
1.
Carbonate compositions from metamorphosed manganese deposits on the binary CaCO) Microprobe analyses of natural (Ca,Mn)CO]-rlch carbonates with their estimated temperaAm = Serra do Navio (Scarpelli, 1970), M = Muretto Pass (Peters et a1. 1980), B = Buri(Peters et a1., 1977), A = Alagna (Peters et a l , , 1980), and S"" Scerscen (Peters et a l , , From de Capitani and Peters (1981). I
Graf, 1957; de Capitani carbonates
and Peters,
in the systems CaC03-MgC03-FeC03 or CaC03Each of these subsystems has been investigated experimentaland other workers
0
than 400 C, and applications Rhombohedral
group
(see Reeder,
dolomite
particularly
to metamorphic
at temperatures
greater
rocks await the petrologist.
carbonates
These may be separated
magnesite
Other metamorphic
are well-described
MgC0 -MnC03• 3 ly by Goldsmith
calcite
1981) (Fig. 1).
into two major
structural
(space group R3c) and the dolomite Chapter
1).
Within
subdivisions,
the
group (space group R3)
the calcite group are calcite
(CaC0 ), 3
(MgC0 ), siderite (FeC0 ) and rhodochrosite (MnC0 ), while 3 3 3 (CaMg(C03)2)' ankerite (CaFe(C03)2)3, and kutnohorite
(CaMn(C0 )2) are contained in the dolomite group4. Two parallel planes 3 through the carbonate tetrahedron, MgC03-FeC03-MnC03, and CaMg(C03)2CaFe(C03) 2-CaMn(C03) 2 , each traverse isostructural solutions and illustrate much of the solid solutions
shown by natural
samples in the carbon-
ate tetrahedron. While this may be taken as the idealized end-member formula for ankerite, the end-member itself is unstable with respect to calcite and siderite. 4 X-ray reflections indicating long-range order are not always observed in kutnohorite (Winter et al., 1981), but the name will be applied in this chapter to compositions near CaMn(C03)2 without requiring this information. The spelling kutnohorite is now preferred to kutnahorite by the I.M.A. and will be used as such in this chapter. 81
./:\
;
:", . .. ....'
\
.. ..
... 7.\ •.. ~ .....
..
'
.
.. _':: .. ::::: .. ::\~\~
.. ...!....OL:
.,
'.
:.,
,_._'.,_,
\
.. . .,: ...i:-'\ ~ .'
I_
..
V .....
:
\
: \f :':':I ... ".: .. : .:.:/::,j:.\ . II'
~::
••
Ie
:,:~.
Figure 2. Carbonate compositions (mol %) in the system MgC03-FeC03MnC03' Carbonates with more than 5 mol % CaC0 are excluded. 3 Data from Doelter (1912,1914,1917), Yosimura (1939) Pal ache et al. (1951), Muta (1957), Deer et al. (1962), Trdlicka (1964), Pisa (1966), Klein (1966,1974,1978), Machamer (1968), Butler (1969). Wenk & Maurizio (1970). Pearson (1974a, b), Beran (1975), Curtis e t; al. (1975), Floran & Papike (1975, 1978), Pinsent & Smith (1975). Klein & Fink (1976), Trdlicka & Hoffman (1976), Kashima & Motamura. (1977), Shimada (1977), Beran & Thalmann (1978), Pekkala & Puustinen (1978). Peters et al. (1977 ,1978), Sanford (1978), Ta1antsev & Sazonov (1979), Haase (1979), Hall (1980), Koba1ski (1980), Sivaprakash (1980), Klein & Gole (1981), Fukuoka (1981), Winter et al. (1981), Frost (1981,1982), Frost et al. (1982), Anovitz & Essene (1983b). I
Carbonates from literature
plotting
close to the plane MgC03-FeC0 -MnC03 are taken 3 The complete solution between MgC0 3 FeC03 and MnC03 is shown by these data. The lack
sources
(Fig. 2)5.
and FeC0 and between 3 of known carbonate compositions been interpreted
by Paulishin
between magnesite and Slivko
and rhodochrosite
(1967) to be a solvus gap.
has This
5 The carbonate compositions in Figures 2 and 3 are taken from hydrothermal and sedimentary as well as metamorphic occurrences because it is often difficult to distinguish these, especially in the older literature. Unlike magnesian calcites and calcian dolomites from sediments, these carbonates show no obvious tendency towards metastable compositions. Plots of the data from undoubted metamorphic occurrences show the same degrees of solid solution but with fewer points. 82
.\
Co Mn (C03)2 ,\
/:. .. ... . ...... . '
..
'._.
..... ... .
:
..
..
:
'
._::_.~:.!'•.:t:u_: ;M"
•• " \~.:: •• ;.:: :.~(./)::;
'.'
.:. :':~" ~,~ ~ ::••..
__
--"'- __
->
Figure 3_ Carbonate compositions (mol %) in the system CaMg(C03)2CaFe(C03)z-CaMn(C03)2. Carbonates with more than 60%or less than 40% CaC03 in
solid
solution
are
excluded
from this
diagram.
Data from Doe1ter (1912,1924,1917), Yosimura (1939), Palache et aL, (1951), Lee (1955), Fronde1 & Bauer (1955), Howie & Broadhurst (1958), Deer et aL, (1962), Trdlicka (1963), L1ambias (1964), Tsusue (1966), Klein (1966,1974,1978), Trdlicka & Sevgu (1968), Butler (1969), Wenk & Maurizio (1970), Pearson (1974a,b), Miyahisa e t e.l. (1975), Pf.nsent; & Smith (1975). Floran & Papike (1975,1978), Filho (1976), Klein s Fink (1976), Shibuya & Harada (1976), Trdlicka & Hoffman (1974,1976), Shimada (1977), Lesher (1978). Pekkala & Paustinen (1978), Sanford (1978), Ta1antsoy & Sazonov (1979). Haase (1979), Van Lamoen (1979), Hall (1980), Koba1ski (1980), Zak & Povondra (1981), Frost (1981,1982), Winter e t; aL, (1981), Irwin (1981), Dill (1983), Anovitz & Essene (1983).
is only permissive rhodochrosites metamorphic geochemical manganese
evidence
with mutual
rocks before
and one would like to find magnesites exsolutions
accepting
or petrological carbonate
deposits
as well as two-phase
this interpretation.
reasons why intermediates contain
calcium which
and
materials
in
There may be are unknown.
is strongly
Most
partitioned
into carbonates
over other phases
(Winter et al., 1981), while few mag-
nesite deposits
carry significant
manganese,
and so there may be few pro-
toliths which would yield magnesite-rhodochrosite 83
compositions.
R3
The
ternary composition
space CaMg(C03)2-CaFe(C03)2-CaMn(C03)2
shown in Figure 3 along with available
carbonate
this plane.
As has long been known,
and ankerite
does not extend completely
analyses
the solid-solution
exceed 2/3 CaFe(C03)2' phase equilibria of Rosenberg
et al. (1962) who found a three-phase content of ankerite
triangle
dolomite
limit appears
and manganoan
in preliminary
the CaFe(C0 )2 3 The
to extend well towards by tielines
kutnohorite. between manganoan
siderite which have been found by Rosenberg
unreversed
two-phase
limiting
of calcite + siderite.
by the coexistence
miscibility
Natural
between
(1960, 1963b) and of Goldsmith
If this is a real gap, it must be penetrated calcite
is
lying close to
to CaFe(C0 )2' and only a few 3 This is generally consistent with the
experimental
ankerite
analyses
(1960)
experiments
materials
on the join CaFe(C0 )2 - CaMn(C0 )2' 3 3 should be sought to confirm this interpreta-
tion. Extensive horite
solid solution occurs among dolomite,
(Fig. 3).
Kutnohorites,
manganoan
mites are more common than generally miscibility
gap between
1976) although ity gap here Stefanova
previous
data.
A more complete
group.
Orthorhombic
carbonates
cerussite
tianites")
of data
set
(Fig. 3) largely
The remaining
complexity
of potential
versus
history
in this long-range
of minerals
petrologic
in
significance6
(CaC03), strontianite
(PbC03), but few instances
in metamorphic
of a miscibil-
1980) based on a more limited collection
of a
et al., 1967; Minceva-
states of short-range
These may have solid solutions aragonite
dolo-
(Shibuya and Harada,
the presence
on the time(t) - temperature(T)
the dolomite
and kutno-
field and at present there is no reason
to suspect a solvus on this join. plane may be due to variable
amongst
suggested
1967; Kobalski,
ankerite
and manganoan
There is no evidence
1960; Minceva-Stefanova
fills the dolomite-kutnohorite
order depending
thought.
and kutnohorite
evaluations
(Rosenberg,
and Gorova,
of carbonate
dolomite
ankerites
rocks.
However,
(SrC0 ), witherite (BaC0 ), and 3 3 of such solid solutions are known
calcian
strontianites
with ~20% CaC03 in solid solution
("calciostron-
are found in sediments
often
6 Alstonite, BaCa(C03)2' is an example. With a structure related to the orthorhombic carbonates, it is presumably the high-pressure form of barytocalcite, and distributions of these two rare polymorphs should have barometric implications.
coexisting Harder,
with calcite
(e.g., Dietrich,
1960; Mitchell
and Pharr,
1964; Salter and West, 1965), and similar compositions
sought in metamorphosed
limestones.
Ore deposits
(Deer et al., 1962) and at L&ngban, carbonates.
Most attention
finer-grained (Sundius,
gangue may contain
1965) which
Sweden
studied with microprobe
1965) contain barium
to vein materials,
two or even three coexisting
should constrain techniques.
should be
in the north of England
(Sundius,
has been directed
1961;
equilibrium
carbonates
relations
In the presence
but the
if carefully
of magnesium,
ben-
stonite (Ba6Ca6Mg(C03)13) or norsethite (BaMg(C0 )2) may occur and these 3 phases may have solid solutions of Pb and Sr for Ba, Mn for Ca, and Fe for Mg (Sundius,
1943, 1965; Sundius
and Blix, 1964; Steyn and Watson,
1967). While
the solid-solutions
carbonates
may indirectly
gaps that petrologists conditions presence
because
are most likely
to gain insight
into metamorphic
is bounded
by the
of the second phase.
The carbonate to have a vertex
IN METAMORPHIC
CARBONATES
tetrahedron
of calcite
CaC03-MgC0 -FeC0 -MnC0 can be considered 3 3 3 (R3d), a base of magnesite-siderite-rhodo-
(R3c), and a plane half-way between vertex and base composed of
the R3 phases dolomite-ankerite-kutnohorite. there are complex from the
and orthorhombic
it is with miscibility
the extent of the solid solution
SOLVUS LIMITS
chrosite
found in rhombohedral
give some information,
R3
solvi in the tetrahedron
plane and both these from the
At metamorphic separating
R3c
base.
temperatures
the calcite vertex Experiments
on two
faces of the tetrahedron, 2) reveal
CaC03-MgC0 -FeC0 and CaC0 -MgC0 -MnC0 (see 3 3 3 3 3 some of these solvi7. We will examine information on
natural
two-phase
assemblages
learned
from them.
Chapter
on these two faces to see what might be
Solvi in the system CaC0 -MgC0 -FeC0 3 3 3 These are reflected two-phase
assemblages
dolomite,
calcite
in natural
carbonate
in the subsystem
- siderite,
dolomite
minerals
forming
equilibrium
CaCO-MgC0 -FeC0 , e.~., calcite 3 3 - magnesite, ferroan calcite -
7 So far there have been no adequate experiments or observations of natural two-phase assemblages constraining connections of these solvi which must occur inside the tetrahedron.
85
ankerite, natural
and ankerite carbonate
function
- magnesian
assemblages
of metamorphic
siderite.
Analyzing
should allow delineation Data from the biotite
zone of the green-
schist facies
(T
=
450°C) (Fig. 4), and the staurolite
zone of the amphi-
bolite
(T
=
5500C)(Fig.
facies
grade.
the coexisting of the solvi as a
5) are taken from Anovitz
(1983a).
While three-phase
reported,
few have been analyzed
Smith,
1975).
Rosenberg detailed
carbonate
assemblages
to the writer's
These have been interpreted
(1960, 1967) and of Goldsmith discrepancies
of the three-phase
(3) the partitioning ankerite - magnesian These inconsistencies
assemblages tioning
1983a).
offer potential
tative results
that of there are
ferroan
calcite
solid
- ankerite
the experimental
and
data
et al., and no simple explanation
or temperature
While
calcite-siderite-
in the magnesite-siderite
are also found in comparing
in terms of pressure
(Barron,
triangle
of Mg/Fe between siderite.
with those of Goldsmith
(Anovitz and Essene,
(Pinsent and
similar
et al. (1962) although
(2) the amount of CaC03 dissolved solutions;
can be made
knowledge
in a manner
been
in:
(1) the location ankerite;
of Rosenberg
and Essene
have occasionally
differences
the natural
as thermometers
1974), the discrepancies
two-phase
in the data ankerite-bearing
in terms of Ca/Mg/Fe must be resolved
before
partiquanti-
can be expected.
Solvi in the system CaC03-MgC03-MnC03 These are not reflected Despite
the experiments
in natural
revealing
two-phase
miscibility
carbonate
assemblages.
gaps in the subsystem
CaC0 -MgC0 -MnC0 (Goldsmith et al., 1962), the writer knows of no equili3 3 3 brium natural two-phase carbonates in this system, although Goldsmith (Chapter
2) and A. M. Gaines
lamellae
and local domains
Franklin-Sterling binary
between
of kutnohorite
an
tetrahedron
R3e
and an
R3
Ironically
kutnohorite difficult
to attain. - magnesian
phase,
to delineate
system to metamorphic
Until equilibrium rhodochrosite
presumably «400°C?)
from the
manganoan
because
the crest
that equilibrium calcite
Moreover,
experimental
is
- magnesian
pairs are found in nature,
or apply the available minerals.
calcite
this is the one
where no solvus has been experimental-
of the solvus is at such low temperatures difficult
1983) have found exsolution in manganoan
Hill area, New Jersey.
in the carbonate
ly located
(pers. comm.,
it is
solvi in this
until the problems
in the
Figure 4. Analyses of carbonates in the system CaCOrMgCOrFeC03from the biotite zone of greenschist facies. Carbonates with >5 mol % MDCD3 are excluded. Crossing tielines presumably mark disequilibrium
pairs
low temperatures.
Figure
5.
Analyses
or
carbonates
reset
at
very
From Anovitz & Essene (1983).
of
carbonates
in
the
system
CaC03-MgC03-FeC03 from the staurolite zone of the amphibolite facies. carbonates with >5 mol % MnC03excluded. From Anovitz & Eaaene (1983).
---87
CaC0 -MgC0 -FeC0 and CaC0 -MgC0 -MnC03 systems are resolvea, only the 3 3 3 3 3 solvus between calcite and dolomite seems presently suited for geothermometry. APPLICATIONS Calcite-dolomite
OF CALCITE-DOLOMITE
thermometry
ditions of metamorphism
THERMOMETRY
is a useful tool for evaluating
con-
because:
(I) calcite and dolomite in marbles binary in metamorphic terranes;
are close to the CaC0 -CaMg(C0 )2 3 3
(2) the thermometer is nearly independent of pressure requiring gross pressure estimates in order to apply a correction;
only
(3) unlike most silicate isograds, it is independent of fluid composition. Its disadvantages are largely related to rapid reequilibration which limits it to minimum estimates of temperature in many rocks. Calcite-dolomite once dissolved metamorphic
thermometry in calcite
temperatures
equilibrated which,
nesian cores of calcites analysis.
is obtained
with dolomite
in turn, is obtained
or reintegrating
While Hutcheon
and Moore
Rice (1977a) have all obtained
the mol % MgC0
by determining
heavily
3
at or near peak by analyzing
exsolved
areas by step
(1973), Bickle and Powell
algebraic
expressions
mag-
(1977) and
for the inferred
temperatures writer
in terms of % MgC03 in calcite (and other parameters), this prefers graphical use of the actual solvus (see Fig. 4, Chapter 2)
to obtain
temperatures,
Goldsmith
and Newton
expressions
combined
(1969), if necessary.
include erroneous
actual P-T-X range for which new experimental
with a small pressure
data.
they were fit and difficulty
because
and is still imperfectly
represent
the dolomite
applications of greater
limb is considerably
of calcite-dolomite than 6500C
calcite grains
in most geological
the
in accomodating is presently
less sensitive
thermometry
(but see Gittins, even exsolved
systems.
to
to temperature
The limits of 400-6500C
are the practical
meter should be applied
in most rocks.
seldom yield
1979) which may dolomite
within
On the other hand, below
solvus limit is not well constrained
and is steep and insensitive
beyond
located.
an upper limit of preserving
4000C the calcite
of dolomite
from
of the algebraic
of the functions
Use of the composition
temperature Careful
Disadvantages
extrapolation
impractical
temperatures
correction
experimentally
(Anovitz and Essene,
1983).
range over which this thermo-
Successful
applications
have been
.500 .530
/~2~
• Ceo Dol o
Ce
':>~':>
o
o Apsley
5Km
L____J
Bannockburn 0
Figure 6a Temperatures obtained from calcite-dolomite thermometry and contoured maximum.temperatures across a segment of Grenville terrane near Bancroft, Ontario. From Sobol (1973).
made to both regional discussed Regional
and contact metamorphic
metamorphic
rocks
Calcite-dolomite
thermometry
rocks by several workers, al. (1973), Hutcheon (1977), Nesbitt
temperatures
temperature isotherms
and Moore
to regional
Sobol and Essene
(1973), Puhan (1980), Nesbitt
metamorphic
(1973), Hatcher
et
(1976), Bickle and Powell and Essene
(1982), and Per-
Sobol and Essene were able to contour approximate
across a region
(Fig. 6).
temperatures
has been applied
including
(1979), Kretz
kins et al. (1982).
Ontario
rocks which will be briefly
below.
While
in the Grenville
it is difficult
terrane near Bancroft,
to determine
whether
or not these
have been reset by perhaps as much as 500C in the higher rocks,
the results
are parallel
(1977) evaluated
agree well with Al Si0 isograds and the 2 5 isograds. Bickle and Powell
with other mapped
the experiments
the influence
of small amounts
thermometry.
They applied
of Goldsmith of FeC0
et al. (1962) to correct
solid solution
3 their model to calcite
89
for
on calcite-dolomite
- ferroan dolomite
pairs
from the Tauern window, Austria, to 490°C for greenschist and Nesbitt
obtaining
reasonable
facies marbles.
and Essene
(1982) in marbles
isograd;
from 425° at the biotite
methods
with dolomite
exsolution
including
(1973), Puhan
al. (1979), and Valley
and Essene
erroneous
in applications
temperatures
al metamorphites.
(1960), Sheppard
erratic results thermometry
of ~5000C
in the N. W. Adirondacks,
where subsequently ranging
Sheppard
and Schwarcz
(1977), Brown et and/or
to region-
relied on X-ray diffraction
temperatures
morphic
Earlier
Graf and Goldsmith
of carbonate
low temperatures
occasionally
isograds.
(1976), Garde
(1980), obtained
The early workers
and as a result obtained
on pelitic
in their carbonates.
(1955), Engel and Engel (1958), Goldsmith and Moore
gave temper-
gave much lower temperatures
On the other hand, various workers,
(1970), Hutcheon
to amphi-
Tennessee,
et al. (1973) using X-ray diffraction
to obtain calcite compositions,
consistent
of 410° (1979)
zone to 540°C at the staurolite
these agreed well with information
work in the same area by Hatcher
of Nesbitt
from the greenschist
bolite facies Murphy Marble belt east of Ducktown, atures ranging
temperatures
Thermometry
methods,
for Grenville
marbles
Brown et al. (1979) obtained
up to 625°C with microprobe
studies.
and Schwarcz calcites
chemically calcites
(1970) showed that X-ray determinations of metasignificantly lower T (by 70-180oC) than bulk 0 calcites. They obtained 645-705 C for bulk analyzed
yielded
analyzed
from the Haliburton-Bancroft-Denbigh-Renfrew
Canada in upper amphibolite isograds.
facies rocks,
area of Ontario,
in good agreement
with silicate
They proceeded
with X-ray determinations of calcites from and obtained scattered temperatures of 175-2800C zone, 230-4350C for the biotite zone, and 290-5750C for
Vermont metamorphics for the chlorite
the staurolite-kyanite reasonable
approximation
values are probably determinations
zone.
The upper temperatures
of peak metamorphic
explained
occasionally
by dolomite
appear
it would be useful
to reexamine
Hutcheon
(1973) applied
and Moore
greenschist-amphibolite Ontario.
ranging
to be successful
this thermometer
exsolved
astride
This isograd
this region and the scattered
in the Vermont
to marbles
carbonate
and obtained
rocks,
methods. from the
terrane near Marble
calcites by microprobe,
content for geothermometry,
isograd.
and the lower While X-ray
these samples by microprobe
3 from 400° to 600°C for marbles
tremolite-calcite
conditions,
exsolution.
facies in the Grenville
They reintegrated
the highest MgC0
of each zone are a
Lake,
selected temperatures
the dolornite-quartz-
should be found at 500-550oC temperatures
are therefore
in
questionable.
Hutcheon and Moore
(1973) also report carbonate
tempera-
tures of ~8000C for marbles
10 km east near the kyanite-sillimanite isograd, too high by perhaps 150-2000C. It would appear that their reintegration
technique
included too many dolomite-rich
primary dolomite
grains.
metry to marbles
in a cordierite-granulite
Damara,
S. W. Africa.
rocks.
Puhan (1976) applied calcite-dolomite
He carefully
calcites and obtained
reintegrated
cores of exsolved
620°C which appears to be some 100°C low for these
Garde (1977) criticized
the general application
after finding calcite compositions
in apparent
dissonance
with silicate
varying
erratically
isograds in greenschist
which yield T of 300-5000C,
3
of carbonate and
facies
His data show calcites with 2-5 mol % MgC0
from W. Greenland.
and 0.2-1.8 mol % FeC0 effect of Fe.
thermo-
facies terrane of Central
thermometry
marbles
areas and/or
3 for the
uncorrected
However by selecting
the maximum MgC0 contents in the 3 the Bickle and Powell correction for FeC0 , his 3 data can be interpreted to show a gradient across the section from 475° calcites and applying
to 5250C in reasonable
agreement with silicate isograds and the regional
grade of metamorphism. amphibolite obtained
Valley and Essene (1980) investigated
to granulite
facies marbles
T < 500°C, suggesting
subsequently
that these high-grade
reset during cooling.
is best suited to greenschist
in the Adirondacks
rocks have been
It appears that carbonate
to middle amphibolite
rocks, and that upper amphibolite
carbonates
do not record peak metamorphic
Contact metamorphic
(1977a, b), Bowman
thermometry
temperatures.
including
Carpenter
(1967), Suzuki (1977), Rice
(1978), Burton and Jackson (1979), Brown
(1980), Bowman
(1982), and Wada and Suzuki (1983) have applied carbonate to contact metamorphic
intruded by high-level X-ray observations
plutons.
aureoles Carpenter
showed extensive
in which carbonate
to infer minimum
temperatures
units are
(1967) noted that optical and
resetting of calcite compositions
and relied on textural evidence of original one-carbonate of 760°C at Crestmore,
is in good agreement with the occurrence
assemblages
California.
This
of other high-temperature
minerals found at Crestmore. Rice (1977a, b) obtained temperatures 0 450-475 C at the tremolite-calcite-quartz-diopside isograd in the Marysville
for
to granulite
rocks
A number of workers,
and Essene
thermometry
facies terranes
regional metamorphic generally
upper
and uniformly
aureole, Montana.
Bowman
(1978) and Bowman and Essene
of
(1980)
Figure tained
500
o
o
100m '-----'
Undifferentiated .ediments
contoured Montana
the temperatures
obtaining
silicate
these appear
Burton and Jackson
syenite
intrusion
the authors accept
the Wind Mountain Wada and Suzuki
carbonates
carbonates
from a contact metamorphic temperatures
gradually
increasing
(1967) data show
by microprobe thermometry
and methods.
to carbonates
in the Kasuga area, Japan.
to 570-6800C at le% MgC03 a < 0.1
Specimen
0
~(~p)
0
~(A)
_£/~
_£(A)
1.2
367.4(1)
4.979(1)
17.111(6)
3.437(2)
6.2
361.67(6)
4.9646(3)
16.944(3)
3.4130(8)
6.5
361.6(1)
4.9635(6)
16.950(4)
3.415(1)
9.1
358.6(1)
4.949(1)
16.904(6)
3.416(2)
Trlpneustes esculentis (test)
10.5
357.4(1)
4.9460(8)
16.869(4)
3.411(1)
Lytechinus varlegatus (test, specimen 2)
11.2
356. 6( 9)
4.9425(9)
16.854(6)
3.410(2)
Lytechinus variegatus (teeth, specimen 1)
11.3
357.4(1)
4.9461(6)
16.871(4)
3.411(1)
Diadema
11.8
355.74 (8)
4.9398(6)
16.834(4)
3.408(1)
12.0
356.2(1)
4.9421(8)
16.840(5)
3.408(2)
12.2
355.71(9)
4.9392(6)
16.837(3)
3.409(1)
Barnacle Diadema (spine,
antillarum specimen
1)
Lytechinus variegatus (spine, Diadema
(spine
(test,
1)
specimen ant illarum
tip,
specimen 1)
antil1arum
specimen 1)
Lytechinus (test,
varlegatus
specimen
1)
Diadema antl11arum (test,
specimen
2)
Homotrema rubrim
12.4
355.99(6)
4.9397(4)
16. 846( 2)
3.4101(7)
Echinometra
lucanter
13.3
353.94(8)
4. 9323( 5)
16.800(4)
3.406(1)
lucanter
13.6
353.9(1)
4.9312(8)
16.803(5)
3.408(2)
(teeth) Echinometra
(test) Lithothamnium ~.
15.5
354.1 (1)
4.9317(8)
16.809(4)
3.408(1)
Amp hiroa ~~.
19.5
349.3(1)
4.9139(8)
16.704(5)
3.399(2)
samples revealed surrounding asymmetric
domains
material.
(~10 µm) up to 10 mol % higher in MgC0
These domains apparently
peaks in the Lithothamnium
contributed
sp. x-ray pattern
than the 3 to the strongly
(cf. Milliman
et al.,
1971) . Previous
microprobe
that small domains within an otherwise al., 1969).
studies of coralline
homogeneous
skeleton
either as high-Mg domains
genic specimen
in this study exhibited
high-Mg
The existence
ever, cannot be excluded.
O'Neill
(1981) suggested
spinulosis,
geneity in the 200
A
sp., no other bio-
domains on a scale that could
analysis.
Echinaster
in the
(Schmalz, 1965; Weber and Kauf-
sp. and Lithothamnium
be detected by microprobe
phase varies on the crystallite
Mg not apparent
(Goldsmith et al., 1955; Milliman
et al., 1971), or as a separate brucite phase Aside from the Amphiroa
have shown may exist
(Moberly, 1968, 1970; Schroeder et
Many algal skeletons contain significant
x-ray patterns,
man,1965).
algae and echinoids
(20-40 µm) of lower or higher Mg concentration
of smaller domains, howthat Mg in the carbonate
size scale (1300-3600 K) in the echinoid
although Blake and Peacor
(1981) demonstrated
size range in the crinoid Neocrinous 110
blakei.
homo-
Moberly
(1970) has
suggested
that brucite domains in coralline
algae are submicron
in
size. Inhomogeneities
on a larger scale were noted during atomic absorption
analyses of the biogenic
Spines of Lytechinus
skeletons.
variegatus have
6.5 mol % MgC03, whereas teeth have 11.3 mol % MgC03• Comparable variations were found in Diadema antiZZarum: tests are 11.8 mol % MgC03, spines are 6.2 mol % MgC03, and spine tips are 9.1 mol % MgC03. Variatioµs in Mg content between tests and spines and within spines were noted for many sea urchins analyzed variations
by Chave
(1954b) and Weber
in the compositions
(1969).
(Table 3).
Chave
variations
(1954b) found compositional
test of one specimen of Lytechinus Substitution could distort
two specimens of Lytechinus
of tests between
variegatus and Diadema antiZZarum
We also observed minor
From 12 diffraction
patterns,
of 3.4 mol % MgC03 within the
variegatus.
of trace amounts of large ions into the biogenic
or increase the size of unit cells.
Sr were all analyzed by electron microprobe, found in quantities
exceeding
volume from substituting made by comparing
but only Sr, Na, and S were
a few hundred ppm.
An estimate of the excess
Sr for Ca in the biogenic
strontianite
50% of the volume discrepancy
and aragonite between
skeletons
K, Ba, Mn, Fe, Na, Sand
magnesia~ calcites was
unit cell volumes.
the biogenic
Only 5 to
phases and the calculated
volume from the results on the synthetic phases could be due to Sr substitution.
This calculated
volume discrepancy
ments caused only local distortion ously in silicates
not be excluded
of the crystal structure as found previ-
above 200 ppm were noticed, but the possibility
by organics or seawater, even after extensive (cf. Blake and Peacor, 1981).
within the crystal volume because
if the trace ele-
(Iiyama, 1974).
Na and S concentrations of contamination
would decrease
structure,
no correlation
they apparently
cleaning,
can-
If these elements are present have little effect on the excess
exists between Na
+
S
+
Sr and the observed
volume deviations. Infrared of O-H bonding
spectroscopic in biogenic
studies discussed magnesian
calcites.
later demonstrate
the existence
As yet, it has not been deter-
mined if the O-H bonding arises from hydroxyl ions or H20 molecules. The presence of hydrated Mg2+ ions in the lattice could increase unit cell volumes. On the other hand, substitution
of OH- for CO~- would probably
cell volume.
The intensity of O-H absorption
the magnesium
content of biogenic
deviations
for biogenic
phases.
phases, however,
nesium concentration.
111
decrease
unit
in the infrared increases with
No trend in unit cell volume is apparent as a function of mag-
The crystal
chemical
and structurally
studies show that biogenic
inhomogeneous.
in skeletal microarchitecture and solubility
phases ~re chemically
These phases also exhibit (Walter, 1983).
large differences
These factors can affect rate
studies and should be kept in mind when interpreting
dissolu-
1
tion data on skeletal magnesian
calcites and solid solution models derived
from these data. SOLUBILITIES Knowledge
of the solubilities
and aragonite, calcites,
AND SOLID SOLUTION BEHAVIOR
and members
is of utmost
these minerals
of the calcium carbonate
in natural
of the CaC03-MgC03 solid solution, the magnesian to an understanding of the behavior of
systems.
The precipitation
Mackenzie,
in numerous
solubility studies
1974; Berner, 1975b;MBller
for magnesian
and Parekh, 1975; Garrels, Wollast,
investigations
1979a; Wollast and
in aqueous
involved dissolution
solutions
' synthetic
including
Ca-Mg-HC0
C02 Besides dissolution, other experimental flow-through
apparatus,
A compilation
of solubility
solubility
determinations
product,
l't g-ca c~ e for solubility
below).
future reference.
ous carbonate
including
and analytical
system.
differences
techniques.
authors
studies.
investigators
is expressed as the I-x x aCa2+ aMg2+ aC032- , has been debated (see
in materials,
Another
possible,
and Busenberg
to problems
solutions,
and
source of divergency
between
is the use of 'different models for the aque-
In Figure II and the remainder
whenever
aqueous model of Plummer In addition
have included use of a
Curves have been drawn through three sets of data for
the results of different
have recalculated,
and seawater.
The large amount of scatter in Figure II undoubtedly
reflects many factors experimental
mag-
water in equili-
by numerous
solubility
IAPM
the use of this expression
discussion
distilled
studies and precipitation
In this diagram,
The major-
of biogenic
solutions,
3 approaches
Ca-Mg exchange
is given in Figure II. stoichiometric
cal-
(e.g., Chave et al., 1962;
data, 1977; Walter and Hanor,
brium with a fixed P
although
product
1980; Walter and Morse, 1983b; Mucci and Morse, 1983a).
ity of experimental nesian calcites
7,
1966; Land, 1967; Schmalz, 1967; Weyl, 1967; Plummer and
and Konig, unpublished Marijns,
behav-
(see Morse, Chapter
at Earth surface T and P are reasonably
Values of the equilibrium
cites have been reported
and dissolution
is fairly well documented
this volume) and their solubilities
Chave and Schmalz,
calcite
importance
ior of calcite and aragonite
well known.
dimorphs,
resulting
112
the experimental
of this section, we data using the recent
(1982). from differences
in experimental
7.2
•
7.4
•
., ] 76 o v
o
° -' I
8.2
11
8.4 8.6
o
11
o
10 20 MOLE %MgC03
30
Figure 11. Summarydiagram of experimental determination of magnesian calcite solubilities. Solubilities are all expressed in terms of -log IAPMg-calcite' The three curves are drawn through the data of Plummer and Mackenzie (1974), the general trend of the dissolution experiment results, and the precipitation experiment results of Mucci and Morse (1983a).
o
!_!..,
Chave.!.!. distilled
~
Chave and
and
A variety
(20
of
.. 1 atm,
2 1966.
Schmalz,
AzIIphiroa
biogenic
lII.te~1als;
+
25·C.
Lytech1nus
eoj e % MgCO);
(11
mole
% MgC03)
sea ....a r e r , Peo
..
Berner,
1975.
Calculation
eqUivalent
in
cent .. in1ng
about
seeded
ahowing
solubility 8.5
of
that
is
c.. lcite
% )'!geo) , using
mole
precipitation
arasonite
to a magnelian
magnesian
data
frolll
calcite.
2
10-3.5
IiiiiJ
1962.
ve t er . PC0
atm,
Sctmalz:,
25·C.
..
1967.
Pinna
(2.5
spines
(10 mole
Hgeo);
distilled
water,
1967.
As above;
% Hgeo»,
% HgC03),
mole and
Amphiroa
(15.4
• 10-0.01
PC0
Lytech1nus ioole
%
•
25"C.
.ttll,
HOller
and Parekh,
ca-Hg
ion
Garrels,
exchange Wollast,
Sphaerech1nus
1975.
From exper1.lllents
behavior
on pure
and Konig,
unpub.
granular
on the
calcite
surfaces
data,
(11 mole % HgCO);
is
.
1977. distilled
2 ~
Schmalz,
distilled
water,
Peo
-
water,
pure
and
spiked
with
ea++
Hg++,
or
P
f)
10-)·5
atm,
Weyl,
1967.
25·C.
()
solution,
1967.
seawater,
IJ
Land,
of
biogenic
of
10-0.01
A variety
biogenic atll'l,
of
distilled
1977).
water,
o
biogenic
A variety Pe0
2
ea++-
Walter
water,
and Hanor,
1979a.
\l
materu1s;
ea r e r La Ls ;
of
6
25"C. by Thorstenson
biogenic
pure
and
Tripneustes
(18 mole spiked
with
% Mf;CO)
(12 mole
% MeCO)
i
distilled
phosphate,
P
C02
- 1 atm,
25·c.
)O·C.
25·C.
water,
and Plul1llller,
seawater,
materials; apparatus,
PCO • 10-0 .. 01 atlll, 2 PlutQlller and Mackenzie, 19710 (revised
distilled •
c02
1967.
-
materials;
and Neogoniol1thon
!low-through
A variety
P
biogenic
)O"e.
A variety
Weyl,1967.
Land,
of
apparatus,
1-1& ++-Heo;
CI
2S·C.
A variety
flov-through
- 1 atm, e02
2
Wollast
spiked
w1th
Walter
and Horae,
water
1 a till , 25"c.
1980.
(5 mole % l1gCO);
tigCO)
materials;
and Harijns.
spines
Sphaerechinus
distilled
CaC12, MeCl2 and NaMeo), 198)b,
and Goniol1thon spiked
with
elypeaster
and
Pe0
solutions
.. 1 atm, %
distilled
HgC1 , P .. 10-2.5 2 e02
25·C.
'Y
l'lIc:ci and Morse, from free with
113
drift
variable
198)(1. experiments;
Ca:l1g ratio,
Incr gan Ic precipitates artificial 25·C.
25·C.
2 (12 mole
(18 ec Le % Hgeo);
Cae12 and
granularis
water
seawater
e tm ,
procedures,
theoretical
matter of debate. difficulties
interpretation
Dissolution
because
of the experimental
experiments,
the incongruent
data has been a
in particular,
are fraught with
nature of the reaction prevents
attain-
ment of equilibrium. In an attempt to clarify the interpretation Thorstenson
and Plummer
(1977) reviewed
of the experimental
the theoretical
criteria
brium between a binary solid solution and an aqueous phase. relationships
derived by Thorstenson
application
to the experimental
results
1978).
Recent experimental
of the equilibrium
1980; Walter,
theoretical
considerations
nesian calcites. thermodynamic
In addition,
properties
from calorimetric
1983; Walter and Morse, 1983b).
Solubilities
of magnesian
several approaches
of experimen-
used to obtain fundamental
calcites are discussed
and new data
calcites
have attempted to determine
As shown in Figure II, many investigators
the solubilities
of magnesian
studies in terms of compositional
(Chave et al., 1962; Land, 1967; Plummer and Mackenzie, dissolution
deter-
are presented.
Dissolution experiments. three most comprehensive
work on solubility
of various solution models to the mag-
of the magnesian
measurements
criteria derived by
involved in interpretation
tal data, and the possible application
1978; work, de-
calcites, has led to contradictory
In this section, we review the experimental mination,
(1974) has been
(Berner, 1978b; Garrels and Wollast,
and Plummer to the magnesian
(Wollast and Marijns,
the
and Plummer appear to be valid, their
and Plummer,
signed to test the applicability Thorstenson
for equili-
Although
data of Plummer and Mackenzie
a source of much argumentation Lafon, 1978; Thorstenson
data,
of biogenic magnesian
calcites
calcites.
The
range studied
1974) all involved
in distilled water saturated with
0.97 atm CO2• Thus, the results of these three studies may be compared directly. We will not consider here the numerous other studies in which values of the equilibrium
solubility product
cites were obtained generally under different
for some single magnesian experimental
conditions
cal(e.g.,
in seawater). Chave et al , (1962) limited their measurements the dissolution
reaction and estimated
the pH at infinite time by extrapola-
tion of plots of pH versus the reciprocal plots were chosen empirically nite time is minerals
approached
calcites, however,
the dissolution
of the square root of time.
reactions
These
they usually yield linear plots as infi-
when calcite, aragonite
are used (Garrels et al., 1960).
case of magnesian because
because
to changes of pH during
or other simple carbonate
Chave et al. claimed that in the
only relative solubilities
are irreversible 114
and therefore
are obtained the material
can have no true equilibrium Solubilities
solubility.
of annealed
skeletal carbonates were estimated
by Land
(1967) by allowing the system to reach a steady state pH and by determining dissolved Ca2+ and Mg2+ concentrations. Dissolution of the magnesian calcites in Land's experiments
appeared
to be congruent
in the sense that the steady
state solution had a molar Ca/Mg ratio similar to that of the solid. At the suggestion the behavior
of Owen Bricker,
of magnesian
calcites during dissolution
of Mg2+ and Ca2+ were monitored
pH and concentrations ments.
They were able to distinguish
reaction
(Fig. 12).
Plummer and Mackenzie
(1974) studied
in greater detail. throughout
up to three stages in the dissolution
The first stage was congruent dissolution,
of the most reactive phase present when the biogenic magnesian were not initially homogeneous
phases.
presumably calcite samples
The congruent portion of dissolution
was followed by a stage in which dissolution
continued but a low magnesium
calcite was precipitated
Solution chemistry
on grain surfaces.
more than a twofold supersaturation 2.
Finally
The
the experi-
indicated
with respect to pure calcite during stage
these authors attributed
stage 3 to the precipitation
of a Ca-rich
phase from the bulk solution. It is interesting dissolution dissolved
to note that the congruency
of the initial step of
is still maintained when the aqueous solution initially contains
Ca2+ or Mg2+ (Fig. 13; Wollast
The distinction
between
tant in the extrapolation
congruent
and Marijns,
and incongruent
of experimental
data.
1980). dissolution
is impor-
Plummer and Mackenzie
extrap-
olated their pH data to infinite time on plots of pH versus the reciprocal
of
the square root of time, as did Chave et al., but used only the congruent portions of the reactions.
They assumed
that the extrapolated
pH values repre-
sented equilibrium
with the initial magnesian calcite composition. These pHs 2 2 were then used, with P and the Ca + and Mg + concentrations, to calculate C02 solubilities from the following expression: (I-x) Ca
2+
+ xMg
2+
23
+ C0
lAPMg-calcite The final pH values obtained during the three studies discussed here are presented ates.
in Figure 14 as a function of the magnesium
Except for the low-Mg calcites,
The lowest pH values, corresponding
to the lowest solubilities,
tically obtained by Land and the highest Plummer
and Mackenzie
assumed
content of the carbon-
there is a large scatter of the data.
values by Plummer
that the lower values reported 115
were systema-
and Mackenzie. earlier provide
,. g
Stag. 2
'1
it I
12
~ _ 10 ~ I ~ ~ I
I-......_ ~ - · .___
E
Q)
0..6
0.7
400
0..01 20.0.
0..8 0.55 ( 10.3/ T , OK)
temperature
19 (above). Pressure-temperature of melting of (a) BaCOr and (b) Data from Baker (1963, 1964).
Figure 20 (right).
en en
... a.
,, 0..5
0.65
diagram in the SrC03-C02 sys-
Pressure-temperature
200
40.0.
600
800
temperature diagram. for Peo,'" lotm PbCo,~
the PbC03-C02 system. Data for phase relations at elevated pressures from Grisafe and White (1964); data for low-pressure sequences from Ball and Casson (1975) and Yamaguchi e t al. (1980).
(OC)
t
t
t
PbCO,PbO3*
PbCO, ~
PbCO,2PbO ~
PbCO,'2PbO
200·
0
of cerussite pressure.
over the range of 200-900 C
Their work is presented
of oxycarbonates
Binary
carbonates
has been designed hedral
and 15 to 1400 bars carbon dioxide
in Figure
20.
The reaction
sequences
(1975) and Yamaguchi
by the
et al. (1980).
systems
Phase equilibria rhombic
co,\ 310.
at 1 atm and less than 1 atm have been supplemented
studies of Ball and Casson
liquid
:::J
0.1
Q)
-2 I-
Figure region tems.
o
SrO •CO2
e
5. _I
~
N
-
o
;; :;!
p..
""o z
II
u
205
All studies concur that the transformation vated nucleation
and growth.
one is immediately
Looking
beyond
struck by the disparity
also in the form and degree of inferred
proceeds
by thermally
acti-
this point of agreement,
not only in absolute
time, temperature,
however,
rates, but
and pressure
depen-
dences. Because activation
of the exponential
energy
(G*), differences
lead to immense differences from laboratory
of absolute
0
(say 400 C)
Thus, even if two investigations
to geologic
measured
identical
energies measured
measured
is nearly
magnitude,
it is understatement
data to natural
occurrences
form derived
dependence
formation
and because
(1965) is excepted1, and Mehl
to describe
energy) and absolute
study of Kunzler
that the major determinants
rates at
absolute
rates
but vary over more than two orders of of these rate
and Goodell
the observed
nucleation.
In all cases, samples with the highest nucleation
transformed
the rate of the transformation
time dependence
variability
most rapidly.
of
in temperature in the careful-
That work demonstrated energy for the bulk trans-
to the opportunity
preferential
of
(1939, 1940,
rates were treated (1970).
of rate and activation
were factors which contributed
rate equations
(1939) and Avrami
The reasons for the remaining
(activation
ly controlled
(say 2000C).
the total range of acti-
to assert that the application
by Johnson
1941) appear to be well-suited the transformation.
temperatures
is made
is problematical.
If the study of Davis and Adams the general
small in Table 1
extrapolation
extrapolated
Because
300 kJ/mole,
near 400°C are not identical
and
rates at 400°C, a differ-
energy of only 30 kJ/mole yields
200°C that differ by an order of magnitude. vation
rate on temperature
in G* which may appear
in rates when the required
temperatures
ence in activation
dependence
for heterogeneous
densities
of sites for
The pressure
is not well characterized,
dependence
but appears
of
to be
small except very near equilibrium.
1 The work of Davis and Adams (1965) contrasts sharply with other studies; the rate functions they employ are purely empirical, so the parameters involvec have no direct physical significance. Their study, however, merits special attention because it is also the only one in which pressures in excess of 3000 bars were utilized. The most unusual feature of their data, and the one which causes their measurements to depart from an Avrami model, is that the rate of transformation levels off and approaches zero before complete conversion is achieved; when these rates are then extrapolated to 99% conversion, extraordinarily long transformation times are required. It appears that the transformation of some appreciable fraction of the reactants is somehow inhibited.
Independent
determination
suggest
that growth kinetics
morphic
aragonite,
extraction
and because
Carlson
and Rosenfeld
spheric pressure
inversion
of nucleation
of calcite 0
the capriciousness
of the geologic
rates independent
375-455 C
are rate-determining
Because natural
textures
in the inversion
of meta-
of nucleation
of growth rate data from bulk transformation
understanding
vations
of growth rates.
measurements
an
of growth
rates.
(1981) measured
crystals
growing
on a petrographic
[Fig. 11].
necessitates
prevents
measurements,
growth rates directly
topotactically heating
Grain diameters
from aragonite
from obserat atmo-
stage over the temperature
range
were found to be linear functions
of
time, and growth rates were found to vary over a factor of about two with crystallographic dation ed.
orientation
of growth due to buildup
The temperature
yielding
migration
s
V
G* ~G T
energy of l63±4 kJ/mole.
(1956) for grain boundary
0 • V • exp(-G*/RT) . [1 - exp(-~G/RT)]
the experimental
to calculate
results
known as functions
determined
Carlson and Rosenfeld,
1981, p. 632-635,
aragonite,
interest,
nucleation
especially
(1983) reanalyzed
as described
The general
Avrami
of nat-
are of considerable transforma-
With this in
(1970) bulk transfor-
theory, using the values
of growth
above.
form of the Avrami
1940, 1941 and Christian,
Although
kinetics
as the aragonite-calcite
and Goodell's
(see
3, this volume).
rates.
of the inversion
for more complex reactions. Kunzler
data in terms of classical
rates measured
Chapter
rates and processes
insofar
tion finds use as a simple model mind, Carlson
and Essene,
determinants
assemblages,
paths for these rocks
rates from bulk transformation
growth rates are the critical ural metamorphic
of aragonite-bearing
pressure-temperature-time
of nucleation
G*, and all other parameters
of P and T, the above equation was used
growth rates during uplift
which in turn constrain
mation
The rate data showed excel-
theory of Turnbull
rate of grain boundary migration; interplanar spacing perpendicular to interface; characteristic atomic vibrational frequency; molar activation free energy; molar free energy difference between aragonite and calcite; absolute temperature; and R = universal gas constant.
Because
theoretical
stress and strain were detect-
of growth rate was found to be exponential,
with the kinetic
are independently
Extraction
drag or retar-
[Fig. 13]:
x =
x
of interfacial
dependence
an activation
lent agreement
where
[Fig. 12]; no effects of impurity
transformation
1975, section 207
4) is:
function
(see Avrami,
1939,
Calcite crystal in monacrys talline aragonite sectioned parallel to (001) produced experimentally by heating on petrographic stage. Note stress-induced lamellar twins and radial fractures; incipient circumferential fractures are visible at lower left. Maximum diameter of crystal, which measures 38 um, is parallel to [100] in aragonite; minimum diameter is parallel to [010] in aragonite. From Carlson and Rosenfeld (1981) .
-13
-13 rGROWTH RATES MEASURED ON
(001) SECTION OF ARAGONITE -14
-14
,..,
r1
U $-15
'0 ~ -15
]
o
-8
o
4
Figure 2. Log rate of calcite dissolution as a function of pH in acids at 25°C. All data are far from equilibrium and independent of P (C02)' The slope is -0.95 and rate may be assumed, within the uncertainties of the data, to be first order in all. Open circle, Tominaga e t a1. (1939): filled circle, Plummer e t a1. (1978); fiJJ.ed square Sjoberg (1978); open star, Wentzler (1971); open square, Berner and Morse (1974); filled star, King and Liu (1933); vertical bar, Wey1 (1958). After Plummer et al. (1979).
6
pH only as an approximation
where activity coefficients
and thermal and electrical Equation The dissolution unit area. matter,
neutrality
9, while relatively rate is dependent
are assumed constant,
effects are minor.
simple, contains
elements for controversy.
on surface area, since the flux is per
For smooth, spherical, non-porous
but for rough, irregularly-shaped
particles
this is a simple
porous materials
carbonates,
it can be very complex
coefficient
is not the same for all components
such as biogenic
(Walter and Morse, 1983a).
The diffusion
involved in the reaction
(e.g., DH+ is several times greater than DCa2+, Robinson and Stokes, ]959). The thickness of the stagnant boundary layer is strongly dependent on hydrodynamic conditions.
It also can depend on particle
size.
A commonly used general equation for dissolution of crystals, similar to Equation
9, is: (10) r
where R is the dissolution
rate, A is the total surface area of the dissolv-
ing solid, and r is particle 1961; Nielsen,
radius
(e.g., Frank, 1950; Terjesen et al.,
1964; Berner, 1971; Berner and Morse, 1974).
demands an essentially tic Le use for particles
infinitely
z s
where A and B are constants.
'
A plot of sin X (called the contrast transfer
function) shows that for a particular Cs there is a value of 6F, defining the Scherzer focus for which the focal and aberration effects tend to annul one another to give a reasonably constant phase shift of electrons, over a range of scattering
angles.
Figure 14 shows calculated contrast transfer
functions for a 500 kV microscope with parameters
very similar to those of
the instrument used to produce Figures 2ge, 33, 42b and 44b.
Images of very
thin crystals formed under these conditions have the correct phase information and are structure images, i.e., they show the distribution potentials projected orientations
denote atomic positions.
Phase effects in images not formed
strictly under these conditions may still be interpretable computer simulations
of atomic
in the beam direction, which for zone axial crystal
(e.g., see Kihlborg,
1979).
In this review we rely on defect identification review of the SEM literature
on sedimentary
318
with the aid of
with the TEM.
carbonates,
For a
the reader is
1.0,-------------
10
-----,
b
a 10
--_._._
-2.0
Figure
14.
Example of
500 kV; Cs• 2.0 incident
referred
contrast
axial
111m,
semi-angle
=
0.4
to Bathurst
transfer
functions
illumination mred ,
focal
=
Reeder
a high
100 A (courtesy
resolution
electron
(b) effect
of
D.J.
microscope
TRANSFORMATIONS
in dolomite
(Chapter 1) has already discussed cation ordering relations
dolomite.
In this section we briefly examine experimentally-induced
structures
that form during the
a change from the calcite-
R3c ~ R3
transformation
to dolomite-type
(1982) used TEM to examine microstructures quenched from above the transformation
structure).
stacking defects and domain boundaries.
absent in samples quenched
from lower temperatures.
image from Reeder and Nakajima in a transformed thicknesses
dolomite.
spanning
tural relationship
only a few cation layers.
transformation.
which occur pervasively
Morphologically,
Figure l5a is a lattice
Although
platelets with their actual struc-
they apparently
reflect
sequences in very localized areas which formed
tified by contrast analysis variant.
in the starting mate-
localized basal stacking defects
is not yet clearly established,
imperfect cation stacking
These dolo-
of the cations,
Both were found to be
These defects are effectively
during the cation ordering boundaries
revealing
dolomites
(~1125°C).
were found to contain two types of defects not present
to
Reeder and Nakajima
of stoichiometric
temperature
in
micro-
(corresponding
mites, having gone from a random to an ordered arrangement
rial--basal
at
of damping functions:
Smith).
(1975). POLYMORPHIC
Cation ordering
for
(a) coheren~ illumination, spread
Figure l5b shows the domain
throughout
as twin boundaries
the specimen.
these curved boundaries 319
They were iden-
(TB's) caused by a rotation resemble APB's
(e.g.,
Figure 15. TEMimages showing ordering defects from a dolomite specimen annealed at 12000C and quenched rapidly. (a) Lattice image of 0003 fringes showing a coherent basal stacking defect terIRinating at a twin boundary (TB) denoted by arrows. Fringes are offset across the TB. (b) Darkfield aicrograph showing twin d01lain microstructure. FrOllReeder and Nakajima (1982).
Fig. 8a) but geometrically
are TB's.
tions, the contrast in adjacent APB it would be the same.
domains across the TB is different;
While APB's correspond
and offset the whole structure
tion around a. but superposes
non-equivalent
(in the case of dolomite,
layers are affected,
(Fig. l6b).
In reciprocal
for an
to a lattice translation
across the boundary
both cation layers and carbonate offset the cation lattice
For at least some operating reflec-
Fig. l6a), TB's only
The twin operation
is a 180° rota-
space this produces no new reflections, reflections.
The presence
twins is confirmed by single crystal x-ray intensity
of transformation
data.
The identifica-
tion of TB's and not APB's suggests that at l125°C only the cations were disordered,
i.e., the C03 groups maintained their ordered arrangement. Notice, however, that in NaN03 (which at lower temperatures is isostructural with calcite) when heated above 275°C, the N03 groups show rotational disorder (Paul and Pryor, 1971). Subsequent ordering of the N03 groups to give the low-temperature, calcite-type structure corresponds to a change in space group (R3m
+
R3c) with a doubling of the c cell dimension
and should result in the formation
of APB's.
As reviewed
(8.41
A
+
16.82
in previous
A),
chap-
ters (1 and 6), there is evidence become rotationally 800° to 1000°C
disordered
(e.g., see Cohen and Klement, 1973; Mirwald,
Salje and Viswanathan, are ordered,
suggesting that the C03 groups in calcite upon heating within the temperature range
1976).
1976, 1979a;
In dolomite, where both cations and anions
several possibilities
exist (e.g., see the discussions
tias et al .• 1979 and Reeder and Nakajima,
by Gra-
1982).
Defects of the kinds found in these annealed and quenched dolomites are 320
TB
Figure 16. Schematic diagrams showing (a) an APBand (b) a TB in a section through a (1120) plane in the dolomite structure. Ca and Hg atoms, open and closed circles respectively, are segregated alternating planes normal to the a-axis. C03 groups are represented by triangles which have been tipped up here to illustrate their different orientations in successive layers. FromReeder and Nakajima (1982). onto
not generally possibility reasonable
found in natural dolomites.
that such microstructures to conclude
the cation ordering conclusion
On this basis, and excluding
may have been destroyed,
that (most) natural dolomites have not passed through
transformation.
Although
this might appear a trivial
in view of the rather high critical ordering temperature,
significant
the
it seems
with regard to the possibility
of metastably-disordered
it is dolo-
mites that subsequently
order.
In this context, the lack of these specific
ordering
defects
in natural dolomites
transformation
ing reactions
occurring
cipitation.
by different mechanisms,
Furthermore,
strictly to the R3c
+
does not preclude order-
such as dissolution-repre-
our review of the experimental
R3 transformation
results pertains
and does not consider changes in
the degree of ordering which may occur. Aragonite
+
calcite transformation
In contrast transformation changes
to the ordering
from orthorhombic
in primary coordination
transitions aragonite
and waa considered
typical example of a reconstructive
show many common features
Gillet and Madon transformed
(1982) have proposed
genetic environments cipitation,
rearrangement. substituting
tion relations
energies.
On the other hand, the
of partial dislocations. mechanism.
aragonite
So far
seems to occur by dissolution-repre-
often contains
is richer in Mg and Fe.
have been described
can be
In most dia-
by chemical changes which accompany
Specifically, calcite
(1961) as a
which requires breaking
(Fig. l7c-f; see also Bragg, 1924).
for such a martensitic
the transformation
as documented
calcite involves
a scheme by which aragonite
into calcite by the movement
there has been no evidence
above, the solid state
by Buerger
transformation,
of primary bonds and has large activation two structures
discussed
to rhombohedral
the structural
traces of Sr while
Nevertheless,
definite
which document that the aragonite
ture exerts some control on the calcite. 321
orientastruc-
CaQ-lime
R 3c
calcite
Fm3m
aragonite
01234A
»
I,
Pmcn ® r:
,---+ [100J=0
.;"., Co
I
e
,1,
J
'I
-
0-
I
I I
(;OlJ
,,
a
[1;-OJ
I.""-c [2110J=0
iI " , [iii I
/
t [111J
e
1
e ~ [OlOJ = b
o
o
0-0
o
[OOlJ
t e
la
0
e
a_}
12
Turner
(1972)
Barber et a1.
(1981) ,
&
UJ f-
s 0 ...l
0
c
slip ·c (0001)
25-700
5
1/3
-v
1/3 of- (i012)
Barber et
25-700
5
1/6
r-(1014}
50-130
300-500
5
> 500
S
"'250-600
170-100
al. (1983) (1981)
Barber et al.
twinning
I
Of (1012 }
they found a homogeneous boundaries
associated
of microstructures
distribution
of Mg throughout
with mosaic structure.
in biogenic materials
tricacies of their subsequent demonstrated
90-100
the usefulness
and noted some tilt
Clearly the characterization
is vital to understanding
stabilization,
of the TEM/STEM
the in-
and these early efforts have microanalysis
approach.
DEFORMATION Deformation
mechanisms
Deformation
is primarily
i.e., calcite, dolomite
of interest
and aragonite.
in the rockforming
The two main rhombohedral
calcite and dolomite -- form large parts of the sedimentary and are therefore pressure
geologically
environments
important;
environments
(Vance, 1968).
information
about deformation
on the rhombohedral knowledge
aragonite
such as sUbduction.zones
biogenic phase in modern sediments
crust
(Brown et al., 1962), as a 5), and unusual geochemical
for aragonite,
calcite and dolomite.
by Table 1, taken .from Wenk 354
varieties--
continental
is found mainly in high
For these reasons and because
carbonates
is summarized
(see Chapter
mechanisms
carbonates,
there is little
we shall concentrate
The present
state of
(1984), which represents
Figure 39. Temperature dependence of c rd t Lca L resolved shear stress for principal tion mechanisms in (a) calcite and (b) dolomite. FromBarber et a1. (1981).
results of laboratory pressure.
experiments
The temperature
on single crystals tested under confining
dependence
of the principal
is illustrated
in Figure 39.
and twinning.
The former, as explained previously,
and movement
Both materials
of dislocations,
and it is difficult
ferent twinning mechanisms. grain boundary
sliding,
can occur, additional modated
In contrast,
need not involve dislocations)
concentrations
their characteristics
by slip
involves the creation stress for the ini-
deformation
to define critical
and the diffusion
mechanisms
twinning
(which
tends to be promoted at stress
At high temperatures,
mechanisms
(see Paterson,
deformation
can deform plastically
so that there is a critical
tiation of slip on each slip system. in principle
deforma-
stresses for the dif-
where dislocation
climb,
of point defects to grain surfaces
occur whereby changes of shape can be accom-
1979; Langdon,
1984, for reviews).
Mechanisms
in calcite and dolomite will now be considered
and in more
detail. Twinning
Cal.o i.t:e,
and especially
on e
=
shear stress) for r-slip is high. also occur
{01I8} occurs readily up to ~500°C
at low temperatures,
for which the crss (critical resolved Minor twinning on rand
(Paterson and Turner, 1970).
(l859), various workers
Following
have studied e-twinning
(for a review see Barber and Wenk, 1979a).
in rhombohedral
carbonates
have a preferred
The sense of a deformation
=
{OlI2} can
in calcite, a classic mineral
in this context
for shear.
f
the early work of Pfaff
Slip and twinning
sense, i.e., a definite direction
is positive,
as defined by Turner et
al. (l954a), if rotations
during glide tend to move the pole of the glide
plane towards the c-axis,
and negative 355
if the pole moves away.
e-twinning
is positive.
Elastic
(i.e., reversible)
twins can also be produced
cite (Garber, 1938, 1947), but these are a curiosity,
irrelevant
in cal-
to plastic
deformation. Rhombohedral
=
slip on r
{l014} , in the negative
over a wide range of temperatures, et al., 1954a) and polycrystals f-slip is also an important somewhat enigmatic;
sense, prevails
as shown by work on single crystals
mechanism.
Despite much work, r-slip remains
in many instances r-slip is not well defined at the TEM
level, the dislocations
commonly being very curved, not lying in well-defined
planes and interacting
strongly with each other, even at low temperatures.
The basic lattice translation
vector in the {l014} planes is 7.7
large for the Burgers vector of a primary
slip system.
cessive glide of two partial
with Burgers vectors
+
i c],
(Turner
(e.g., Turner et al., 1956; Wenk et al., 1973).
i.e., half of 7.7
A
dislocations
K
long,
Slip via the suc[jal + ja2
in length, is possible, which would give stacking
faults in the C03 sublattice. produced no concrete evidence
But TEM and HREM investigations for the mechanism.
have so far
There is little evidence
for the operation of other slip systems, although Turner and Orozco
(l976)
have reported a case of basal slip. Flow laws have been determined marbles
(e.g., Heard and Raleigh,
1977; 1980).
for fine-grained
1972; Rutter,
limestones
For high strain rates at low temperatures, .
exponentially-dependent
on stress, G (E
=
and coarse
1972; 1974; Schmid et al., strain rate ~ is
exp CG) with C ~ 2.5 kbar
-1
for
Solnhofen limestone at
... ... ...... QI'"
...u ~ .. ..." U
.. 0
...." ".. ".., 0>
.... QI
~ §
.... ~~ ..... ~
I
0
....
,"... -e ...
e-,
...::r
....~'" QI
::r
....... ~'"
358
Biaxiality metamorphic
rocks and also in carbonatites
attributed
moderate-to-strong
rally-deformed lamellae
in calcites2 from all grades of
is known to be widespread
calcites
biaxiality
(Turner, 1975a).
to overlap between optically-visible
and the host crystal.
Hauser and Wenk
the optical properties
of submicroscopically-twinned
suggested
that strong biaxiality
was largely attributable
(1975b) concluded
attributed
that slight biaxiality
He also concluded
a model that calcite and
to this effect.
(5° < 2V < 10°) could not be had a submicro-
that in natural rocks, biaxiality
late and minor strain effect of no general geological cance.
thin e-twin
to (optically) visible twinning and, by inference,
scopic origin.
The findings of Barber and Wenk
(l975b)
and natu-
(1976) proposed
predicted
Turner
Turner
in both experimentally-
or petrogenic
was a signifi-
(1979a) may somewhat question
these
views, however,
since they found that a strongly biaxial calcite
(2V ~ 45°)
showed evidence
of repeated
(Fig. 40b).
submicroscopic
twinning and recovery
The calcite also contained high dislocation boundaries,
which were not incorporated
(l976), nor anticipated
e-twinning
tion on naturally-deformed lent.
and many sub-grain
by it.
In calcite mylonites, axial symmetry,
densities
into the model of Hauser and Wenk
which show very strong textures approximating is often pervasive,
but the more sparse informa-
dolomites
that f-twinning
indicates
Both findings are in general accord with experimental
temperature
relationships.
Weiss
is not preva~
data on twinning-
(l954) showed that crystallographic
orienta-
tions of e-twins and the a-axis for each grain in a deformed aggregate be used to determine and the resultant
the net compressive
strain directions.
tally with Yule marble
to
could
and tensile stresses which had acted
The method has been tested experimen-
(Borg and Turner, 1953) and can be applied
to geologi-
cal formations
(e.g., Weiss, 1954; Groshong,
since twinning
occurs at low stresses in calcite and may therefore postdate
a main deformational Other defects
event.
in deformed carbonates
A comprehensive be premature
description
of dislocation
in the light of current knowledge
more space than is available.
Dislocations.
behavior
however,
359
occupy
and comparisons
of
several problems.
There are marked differences
is uniaxial.
would
and this section includes recent
to help in resolving
perfect calcite
in carbonates
and would undoubtedly
Some general observations
calcite and dolomite are possible, HREM results which promise
2 Structurally
1972), although with caution
in the general appearance
of dislocation temperatures,
microstructures as mentioned
in calcites and dolomites
earlier, and exemplified
(Barber and Wenk, 1976; 1979b; Barber, Kohlstedt, products
in TEM observations
1977; Barber et al., 1981; Goetze and
1977; White and White, 1980).
of r-slip,
deformed at low
Dislocations
are far less regimented
in calcite, mostly
and crystallographically
trolled than those in dolomite deformed under comparable is especially acteristic
conditions.
This
true for dolomite yielding by c-slip, which has a quite char-
appearance,
with well-defined
slip planes (commonly in slip bands)
and long straight
mainly-screw
r-slip in calcite
and c- and f-slip in dolomite,
segments of dislocation.
dolomite is most common at higher temperatures are not so straight deformed natural
Heavily-strained
with dislocation
Figures 4la,b,c show
respectively.
f-slip
in
(>300°C) and the dislocations
as basal plane dislocations
calcites of low metamorphic
are very high, so high that individual guish.
con-
at low temperatures.
grade the dislocation
dislocations
are difficult
In many
densities to distin-
laboratory
densities
specimens have the same characteristics, 2 ~lOlO cm- . Such high densities are extremely
uncommon in dolomites. TEM evidence more difficult
and flow stress data (Table l) suggest that r-slip may be
to initiate in calcite at low temperatures
at 300°C) than c-slip is in dolomite is the reason, in calcite
dislocations
generated
(the crss is 64 MPa
Whether or not this
by r-slip at low temperatures
«200°C)
spread laterally out of the slip planes, causing much interaction
with the generation type of behavior
f
deformed
dislocation
of many small dislocation
are easy to identify up to 700°C. specimens of both carbonates
microstructure.
at high temperatures in dolomites
loops and other debris.
is not found in dolomite until ~400°C, although
slip planes, cand prevalent,
(50 MPa at 25°C).
deformed
Twinning
below 300°C.
When climb becomes
are more closely similar in
is more prominent
(>600°C) than in calcites,
This
the active
in dolomites
deformed
and it does not occur at all
Work on experimentally-deformed
samples
(Barber and Wenk, 1979a; Barber et al., 1981) shows that dislocations more likely to be created by twinning in calcite than in dolomite. tions involved
in both c- and f-slip in dolomite
as described
in the next section.
dissociation
in calcite.
Stacking faults.
In dolomite
and those on
analyzed by the methods
f
crystals
deformed between
Figures
contrast
for
300 and 500°C,
those on .a always terminating
much less frequently.
of diffraction
(Barber et al., 1981; 1983).
Disloca-
into partials,
So far there is no certain evidence
long faults are visible on the a- and f-planes, at dislocations
can. dissociate
are
The a-faults are easily
(Barber et al., 1978) and HREM
42a and b show low and high resolution
Figure 41. (a) Dislocations created by r-slip in calcite deformed at 25°C. (b) Dislocations created by a-slip in dolomite deformed at 500°C, (c) Dislocations created by r-slip in dolomite deformed at 800°C (minor r-slip also present), (d) Climbing dislocations associated with a-slip in dolomite deformed at 700°C. (AlII MeV micrographs). 361
."...o :