Table Of ContentFeldspars and Their Reactions
NATO ASI Series
Advanced Science Institutes Series
A Series presenting the results of activities sponsored by the NA TO Science Committee,
which aims at the dissemination of advanced scientific and technological knowledge,
with a view to strengthening links between scientific communities.
The Series is published by an international board of publishers in conjunction with the
NATO Scientific Affairs Division
A Life Sciences Plenum Publishing Corporation
B Physics London and New York
C Mathematical Kluwer Academic Publishers
and Physical Sciences Dordrecht, Boston and London
D Behavioural and Social Sciences
E Applied Sciences
F Computer and Systems Sciences Springer-Verlag
G Ecological Sciences Berlin, Heidelberg, New York, London,
H Cell Biology Paris and Tokyo
I Global Environmental Change
NATO-PCO-DATA BASE
The electronic index to the NATO ASI Series provides full bibliographical references
(with keywords and/or abstracts) to more than 30000 contributions from international
scientists published in all sections of the NATO ASI Series.
Access to the NATO-PCO-DATA BASE is possible in two ways:
- via online FILE 128 (NATO-PCO-DATA BASE) hosted by ESRIN,
Via Galileo Galilei, 1-00044 Frascati, Italy.
- via CD-ROM "NATO-PCO-DATA BASE" with user-friendly retrieval software in
English, French and German (© WTV GmbH and DATAWARE Technologies Inc.
1989).
The CD-ROM can be ordered through any member of the Board of Publishers or
through NATO-PCO, Overijse, Belgium.
Series C: Mathematical and Physical Sciences -Vol. 421
Feldspars and Their Reactions
edited by
lan Parsons
Department of Geology and Geophysics,
The University of Edinburgh,
Edinburgh, United Kingdom
....
"
Springer-Science+Business Media, B.V.
Proceedings of the NATO Advanced Study Institute on
Feldspars and Their Reactions
Edinburgh, United Kingdom
June 29-July 10, 1993
A C.I.P. Catalogue record for this book is available from the Library of Congress
ISBN 978-94-010-4483-7 ISBN 978-94-011-1106-5 (eBook)
DOI 10.1007/978-94-011-1106-5
Printed on acid-free paper
AII Rights Reserved
© 1994 Springer Science+Business Media Dordrecht
Originally published by Kluwer Academic Publishers in 1994
Softcover reprint ofthe hardcover lst edition 1994
No part of the material protected by this copyright notice may be reproduced or
utilized in any form or by any means, electronic or mechanical, includ ing photo
copying, recording or by any information storage and retrieval system, without wriHen
permission from the copyright owner.
TABLE OF CONTENTS
Preface xix
Acknowledgements xx
Frontispiece xxi
Institute Participants xxii
1. THE CRYSTAL STRUCTURES OF THE ALUMINIUM-SILICATE
FELDSPARS 1
PAUL H RIEBE, Department of Geological Sciences, Virginia Polytechnic
Institute & State University, Blacksburg, Virginia 24061-0420, U.S.A.
Abstract 1
1. Introduction 1
1.1 HISTORICAL PERSPECTIVE 1
1.2 RECENT PROGRESS AND OVERVIEW 2
2. Chemistry of Feldspars 3
3. Topology of the Feldspar Framework 4
4. Patterns of AI, Si Order-Disorder: Space Groups 6
4.1 ALKALI FELDSPARS 7
4.1.1 Monoclinic (C2/m) K-richAlkali Feldspars 8
4.1.2 Triclinic (Cl) K-rich Alkali Feldspars 10
4.1.3 Room-Temperature Phase Transition in Low Microciine? 10
4.1.4 Triclinic (Cl) Anorthoclases, K-Analbites, and the Transition to
C2/m Na-Sanidines 10
4.1.5 Triclinic (Cl) Low, Intermediate, and High Albite 11
4.1.6 Analbite and the Transition to C2/m Monalbite 12
4.2 CELSIAN AND HY ALOPHANE 12
4.3 ANORTHITE AND INTERMEDIATE PLAGIOCLASES 13
4.3.1 The 'Aluminium Avoidance' Principle and AI, Si order/disorder 13
4.3.2 Primitive Anorthite 15
4.3.3 Pseudo-symmetry and the Average Structure Concept 17
4.3.4 Body-centered Anorthite 19
4.3.5 Intermediate Plagioclases 20
5. The M Cations in Feldspar Structures 21
5.1 POTASSIUM IN SANIDINES AND MICROCLINES 21
5.2 SODIUM IN ALBITES 24
5.2.1 Sodium in Low Albite 24
5.2.2 Sodium in High Albite and Monalbite 24
5.2.3 Sodium in Intermediate Albite (IA) and Na/Ca in Sodic Plagioclase 25
5.2.4 CaiNa in Calcic Plagioclase 26
6. Average Structures of Feldspars Represented by Cell Parameters:
the Temperature-Pressure-Composition Analogies 28
vi
6.1 CHANGES IN VOLUME WITH P, T, X 28
6.1.1 Compressibility and Phase Changes with Pressure 28
6.1.2 Thermal Expansion 30
6.1.3 Variation oj Composition in 'Solid-Solution'Series 30
6.2 CHANGES IN CELL DIMENSIONS WITH P, T, X 33
6.2.1 Series oj Na-and K-Mixed with Ca-, Sr-, and Ba-feldspars 33
6.2.2 The M2+ -feldspars 33
6.2.3 Alkali Feldspars 38
6.3 CHANGES IN T-O-T ANGLES AND M-O DISTANCES WITH
P,T,X 38
6.3.1 Disordered Alkali Feldspars 38
6.3.2 Ordered Alkali Feldspars and the Structure oj Low Albite at 5 GPa 38
7. Future Work 44
References 44
2. ASPECTS OF ALKALI FELDSPAR CHARACTERIZATION:
PROSPECTS AND RELEVANCE TO PROBLEMS OUTSTANDING 51
ACHILLE BLASI and CARLA DE POL BLASI, Department of Earth Sciences,
University of Milano, Via Botticelli 23, 20133 Milano, Italy
Abstract 51
1. Introduction 51
2 Light Optics 51
3. Composition and Lattice Strain 53
3.1 COMPOSITION OF UNSTRAINED FELDSPARS 53
3.2 STRAINED FELDSPARS 54
3.2.1 Background 54
3.2.2 Determination oj Lattice Strain 55
3.2.3 Determination ojComposition 57
3.3 COMPOSITION FROM K, Na SITE REFINEMENTS OF X-RAY
INTENSITY DATA 60
4. Determination of Tetrahedral AI Contents in Alkali Feldspars 64
4.1 T-SITE OCCUPANCIES FROM LATTICE PARAMETERS 64
4.2 T-SITE OCCUPANCIES FROM T-O DISTANCES 70
4.3 T-SITE OCCUPANCIES FROM Si, Al SITE REFINEMENTS
OF X-RAY INTENSITY DATA 76
5. Single-Crystal X-ray Diffraction Patterns and Relationships with
TEM Techniques 83
5.1 THE DIAGONAL ASSOCIATION 84
5.2 THE ANTIDIAGONAL ASSOCIATION 89
5.3 P2/a STRUCTURAL ARRANGEMENT 90
6. Unanswered questions and suggestions for future work 92
Acknowledgements 94
References 94
vii
3. PHASE TRANSITIONS AND VIBRATIONAL SPECTROSCOPY
IN FELDSPARS 103
E K H SALJE, Department of Earth Sciences, University of Cambridge
Downing Street, Cambridge CB2 3EQ, England
Abstract 103
1. Introduction 103
2. Phase Transitions and Order Parameters 105
2.1 THE ORDER PARAMETER 105
2.2 COUPLING BETWEEN ORDER PARAMETERS 106
2.3 SOME TYPICAL LANDAU POTENTIALS 108
3. Kinetic and Other Non-Equilibrium Behaviour 112
4. Hard Mode Phonon Spectroscopy 114
4.1 INTRODUCTORY REMARKS ON OPTICAL SPECTROSCOPY 114
4.2 SOFT MODES VERSUS HARD MODES 117
4.3 THE CHARACTERISTIC LENGTH SCALE 119
4.4 HOW TO DO IT 120
5. Applications and Examples 122
5.1 TEMPERATURE DEPENDENCE OF HARD MODES IN ALBITE 122
5.2 EFFECT OF THE C2/m-CT TRANSmON IN ANORTHOCLASE 124
5.3 A DISPLACIVE PHASE TRANSITION WITH SOME
FLUCTUATIONS: pI-Ii IN ANORTHITE 125
5.3.1 Space Average Model 125
5.3.2 The Ca-jumping Model 126
5.3.3 Soft-mode Model 127
5.4 DETERMINATION OF THE DEGREE OF AI, Si ORDER IN Na
FELDSPAR 133
5.5 STRUCTURAL MODULATIONS IN NATURAL POTASSIUM
FELDSPAR 136
5.6 ON THE EFFECT OF Na-K MIXING AND THE STUDY OF
EXSOLUTION: AN OUTLOOK 143
Conclusion 148
Acknowledgements 148
Appendix 1
DEVIATION OF THE GIBBS FREE ENERGY FOR A PHASE
TRANSITION WITH CONTINUOUS LOCAL POTENTIALS 149
Appendix 2
ON THE INTERCORRELATION OF AI, Si ORDERING AND THE
GENERATION OF SPONTANEOUS STRAIN 153
References 155
viii
4. PARTIAL MELTING REACTIONS OF PLAGIOCLASES AND
PLAGIOCLASE-BEARING SYSTEMS 161
W JOHANNES, J KOEPKE and H BEHRENS, Institut fUr Mineralogie,
Universitat Hannover, Welfengarten 1, D-30167 Hannover, Gennany
Abstract 161
1. Introduction 161
2. Previous Work on Plagioclase-melt Interaction 162
3. Starting Materials and Experimental Procedure 163
4. Experimental Results and Discussion 165
4.1 DRY MELTING OF PLAGIOCLASE An68 AT 14200C 165
4.2 WET MELTING OF PLAGIOCLASE AT P = 5 Kbar 174
4.3 THE INFLUENCE OF ADDITIONAL COMPONENTS AND
PHASES 181
4.3.1 Melting Reactions in the System Qz-Ab-An-HzO 182
4.3.2 Melting Reactions in the System Qz-Ab-An-AlzOrHzO 182
4.3.3 Melting Reactions in the System Qz-Or-Ab-An-HzO 188
4.3.4 Kinetics ofp artial melting in systems with additional
SiOrcontaining phases beside feldspars 191
5. Summary 193
Acknowledgements 193
References 193
5. TERNARY FELDSPARIMELT EQUILmRIA: A REVIEW 195
H NEKVA SIL, Department of Earth and Space Sciences, State University
of New York, Stony Brook, NY 11794-2100, U.S.A.
Abstract 195
1. Introduction 195
2. Ternary Feldspar Geothermometry 196
2.1 ACTIVITY MODELS FOR TERNARY FELDSPAR SOLID
SOLUTIONS 196
2.2 GEOTHERMOMETRY: CALCULATION METHODOLOGY
AND RESULTS 201
3. Ternary FelsparlMelt Equilibria 203
3.1 LIQUIDUS RELATIONS IN THE FELDSPAR SYSTEM 204
3.2 COMPOSmONAL EVOLUTION OF FELDSPARS DURING
CRYSTALLIZATION 210
3.2.1 Equilibrium Crystallization 210
3.2.2 Fractional Crystallization 215
4. Conclusions 217
5. Acknowledgements 217
6. References 217
ix
6. SUBSOLIDUS PHASE RELATIONS OF THE PLAGIOCLASE
FELDSPAR SOLID SOLUTION 221
M A CARPENTER, Department of Earth Sciences, University of
Cambridge, Downing Street, Cambridge, CB2 3EQ, England
Abstract 221
1. Introduction 221
2. A Possible Phase Diagram 226
3. Lines of Evidence 227
3.1 ORDERIDISORDER EXPERIMENTS 227
3.1.1 C21m = cI Transition 228
3.1.2 ci = II Transition 228
3.1.3 II = e1 Transition 228
3.1.4 ci = e2 Transition 232
3.1.5 Ordering within the CI stability field 232
3.1.6 IT = PTTransition 232
3.1.7 Summary 232
3.2 MICROSTRUCTURES 233
3.2.1 Peristerite gap 233
3.2.2 B¢ggild gap 233
3.2.3 Huttenlocher gap 236
3.3 COMPOSITIONS OF COEXISTING CRYSTALS 238
3.3.1 Coexisting Phases across the Peristerite Gap 238
3.3.2 Coexisting Plagioclases with Intermediate Compositions 240
3.3.3 The Low Temperature Assemblage Albite + Anorthite 241
3.4 PROPERTIES OF THE INCOMMENSURATE "e" STRUCTURE 241
3.4.1 Mestable Incommensurate Structure ofA northite 241
3.4.2 Structure of "e" Plagioclase 243
3.4.3 Influences of Temperature and Composition 246
3.4.4 Distinction between eland e2 Structures 247
3.5 THERMODYNAMIC DATA 248
3.5.1 Enthalpies of Ordering and Mixing 248
3.5.2 Energetics ofA ntiphase Boundaries 250
3.5.3 Ion-exchange Data 252
3.6 KINETIC CONSTRAINTS 254
4. The Rudiments of a Thermodynamic Model 255
4.1 SCHEMATIC G-X CURVES 255
4.2 LANDAU FREE ENERGY EXPANSIONS 259
5. Conclusion 260
5.1 AJJSi ORDERING AT Ano -An 261
l5
5.2 LOCAL ORDERING IN THE C1 SOLID SOLUTION 261
5.3 MICROSTRUCTURAL EVIDENCE FOR SPLIT BEHAVIOUR
AT-Ans2 261
5.4 ci = e2 TRANSITION TEMPERATURES 261
5.5 THE II = el ORDERING TRANSITION 261
5.6 THERMODYNAMICS OF INCOMMENSURATE ORDERING 262
x
5.7 INCOMMENSURATE STRUCTURES AND DIFFERENCES
BETWEENe] AND e2 ORDERING 262
5.8 PHASE EQUILIBRIUM AND ION-EXCHANGE EXPERIMENTS 263
Acknowledgements 263
References 263
7. FELDSPARS AT IDGH PRESSURE 271
R J ANGEL, Department of Geological Sciences, University College
London, Gower Street, London, WClE 6BT, England
Abstract 271
1. Introduction 271
2. Stability of Feldspars at High Pressure 272
2.1 ALBITE 272
2.2 K-FELDSPAR 274
2.3 ANORTHITE 276
3. Compressional Behaviour 279
3.1 BULK MODULI 279
3.2 UNIT CELL PARAMETER VARIATION WITH PRESSURE 285
3.3 STRAIN TENSORS 287
4. Structural Phase Transitions 291
4.1 PHASE TRANSmONS IN ALKALI FELDSPARS 291
4.2 PI TO 11 TRANSITION IN ANORTHITE 293
4.2.1 PI =I Ii n End-Member Anorthite 295
4.2.2 Effect ofA I, Si Disorder on P J =I i 298
4.2.3 Effect ofA lbite Substitution on pj =I IT ransition 301
4.2.4 Phase Diagramfor Anorthite PI =I I Transition 303
4.2.5 Thermodynamic Analysis 304
4.3 PHASE TRANSITIONS IN OTHER FELDSPARS 306
4.4 CONCLUSIONS 307
5 Acknowledgements 307
6. References 307
8. RECENT WORK ON OSCILLATORY ZONING IN PLAGIOCLASE 313
T H PEARCE, Department of Geological Sciences, Queens University,
Kingston, Ontario, Canada K7L 3N6
Abstract 313
1. The Problem 314
2. Empirical Observations of Zoning 315
2.1 HYPOTHESES AND ASSUMPTIONS 315
2.1.1 Crystal Growth 317
2.1.2 Analysis of Zoning Patterns 317
