Chromium: Its Physicochemical Behavior and Petrologic Significance (eBook)

Front Cover 1
Chromium: Its Physicochemical Behavior and Petrologic Significance 2
Copyright Page 3
Table of Contents 4
FOREWORD 6
Chapter 1. Phase relations in chromium oxide-containing systems at elevated temperatures 8
INTRODUCTION 8
PHASE BELATIONS IN SELECTED CHROMIUM OXIDE-CONTAINING SYSTEMS 9
Chapter 2. The system chromium–oxygen at high oxygen pressures 
30 
INTRODUCTION 30
PHASE RELATIONS 31
CHARACTERIZATION OF THE PHASES 37
COMMENTS ON THE STABILITY OF TETRAVALENT CHROMIUM 42
Chapter 3. Thermochemistry of chromium compounds, especially oxides at high temperature 46
INTRODUCTION 46
CHROMIUM METAL, ITS ALLOYS, AND OXIDATION STATE OF THE METAL 46
HIGH TEMPERATURE OXIDE CHEMISTRY OF CHROMIUM 50
Chapter 4. Solid oxide electrolyte emf cell determination of the standard free energy of Cr2O3 and applications to chromium-bearing mineral systems 
60 
INTRODUCTION 60
STANDARD FREE ENERGY OF FORMATION OF Cr2O3 
60 
EXPERIMENTAL TECHNIQUE FOR MEASUREMENT OF FREE ENERGY RELATIONSHIP 61
EXPERIMENTAL RESULTS 62
DISCUSSION 66
SOLID ELECTROLYTES FOR THERMOCHEMICAL MEASUREMENTS IN CHROMIUM-BEARING MINERALS 67
SUMMARY 70
Chapter 5. Preparation of Cr2O3 crucibles and the defect structure of Cr2O3 
74 
INTRODUCTION 74
METHOD 74
DISCUSSION 76
Chapter 6. Smelting chrome ore 80
INTRODUCTION 80
SMELTING REACTIONS 80
CARBON CONTENT OF FERROCHROME ALLOYS 81
CONCLUSION 83
Chapter 7. Crystal field effects in chromium and its partitioning in the mantle 84
INTRODUCTION 84
CRYSTAL FIELD ENERGIES 84
FRACTIONATION OF CHROMIUM IN THE MANTLE 87
Chapter 8. Crystal-field effects in spinel: oxidation states oî iron and chromium 92
INTRODUCTION 92
EXPERIMENTAL METHODS 92
CRYSTAL-FIELD EFFECTS 93
SPECTRA AT HIGH PRESSURE 98
ASSIGNMENT OF BANDS OF Fe2+, Fe3+, Cr2+ AND Cr3+ IN SPINEL 
100 
INTERPRETATION OF THE CHEMICAL HISTORY OF THE SPINELS 103
Chapter 9. Trivalent and divalent chromium ions in spinels 104
INTRODUCTION 
104 
EXPERIMENTAL PROCEDURES 104
RESULTS AND DISCUSSION 105
Chapter 10. Magnetic properties of chromium chalcogenide spinels 112
CRYSTALLOGRAPHY 112
MAGNETIC PROPERTIES 112
CONCLUSIONS 116
Chapter 11. Magnetochemical characterization of Fe(FexCr2_x)O4 spinels 
118 
INTRODUCTION 118
BACKGROUND TO MAGNETIC HYSTERESIS CHARACTERISTICS 120
EXPERIMENTAL RESULTS 122
DISCUSSION AND CONCLUSIONS 127
Chapter 12. Mineralogy of chromium 132
Chapter 13. Distribution and significance of chromium in meteorites 
140 
INTRODUCTION 140
BULK CHROMIUM IN METEORITES 142
CHROMIUM IN METEORITIC MINERALS 142
SIGNIFICANCE OF CHROMIUM CONCENTRATION AND DISTRIBUTION IN METEORITES 155
Chapter 14. Chromium and the genesis of diamond 160
INTRODUCTION 160
OLIVINE 160
CHROMITE 162
CHROME–DIOPSIDE 
163 
CHROME–PYROPE 
163 
CHROMIUM IN DIAMOND 164
Chapter 15. Chromite spinels from ultramafic xenoliths 168
INTRODUCTION 168
TEXTURAL TYPES 168
CHEMISTRY OF THE CHROMITE SPINELS 174
DISCUSSION 176
Chapter 16. Coexisting spinel and silicates in alpine peridotites of the granulite facies 180
INTRODUCTION 180
THE SEIAD ULTRAMAFIC COMPLEX 180
THE FINERO ULTRAMAFIC MASS 182
COMPARISON OF THE SEIAD AND FINERO COMPLEXES 184
MINERAL CHEMISTRY 185
ELEMENT PARTITIONING 188
CONCLUSIONS 191
Chapter 17. Chrome-spinel in progressive metamorphism— a preliminary analysis 192
INTRODUCTION 192
METAMORPHIC PARAGENESES OF CRUSTAL ULTRAMAFIC ROCKS 193
ANALYTICAL METHOD 193
PROGRESSIVE COMPOSITIONAL CHANGES 193
CONTROLS ON COMPOSITION 196
Chapter 18. The paragenesis of zoned chromite from central Manitoba 206
INTRODUCTION 206
GEOLOGICAL SETTING 206
MINERALOGY 210
COMPOSITIONAL VARIATION IN CHROMITE 215
ORIGIN OF ZONED CHROMITE IN CENTRAL MANITOBA 217
SUMMARY AND CONCLUSIONS 222
Chapter 19. Crystallization sequences in the Muskox intrusion and other layered intrusions—II. Origin of chromitite layers and similar deposits of other magmatic ores 
226 
INTRODUCTION 226
GEOLOGY OF THE MUSKOX INTRUSION 227
FRACTIONATION OF NICKEL AND CHROMIUM IN SILICATE MELTS 234
FORSTERITE-PlCROCHROMITE CRYSTALLIZATION ON THE JOIN MgO.SiO2–Cr2O3–K20.6SiO2 237
FORMATION OF CHROMITITE LAYERS 238
SUPPORTING EVIDENCE AND DISCUSSION 243
APPLICATION OF THE CONTAMINATION MECHANISM TO OTHER TYPES OF MAGMATIC ORE DEPOSITS 251
CONCLUSIONS 255
Chapter 20. Postcumulus and subsolidus equilibration of chromite and coexisting silicates in the Eastern Bushveld Complex 258
INTRODUCTION 258
MATERIALS AND METHODS OF INVESTIGATION 260
TERMINOLOGY 260
CHROMITE IN CHROMITE–OLIVINE CUMULATES 
261 
CHROMITE AND BRONZITE IN BRONZITE–CHROMITE CUMULATES 
264 
CHROMITE IN CHROMITE CUMULATES (CHBOMITITES) 266
DISCUSSION 266
CHROMITE IN CHROMITE–PLAGIOCLASE CUMULATES 
268 
Chapter 21. Reaction trends shown by chrome-spinels of the Rhum layered intrusion 274
INTRODUCTION 274
RESULTS 280
REACTION MECHANISMS 283
DISCUSSION AND CONCLUSIONS 285
Chapter 22. A comparison of chrome-spinels in ophiolites and mantle diapirs oî Newfoundland 288
INTRODUCTION 288
GEOLOGICAL SETTING 288
THE BAY OF ISLANDS AREA 289
THE GANDER RIVER BELT 292
BURLINGTON PENINSULA 295
CHROMITE CHEMISTRY 296
INTERPRETATION 301
Chapter 23. A hypothesis of origin for podiform chromite deposits 304
INTRODUCTION 304
FIELD RELATIONS 304
CHROMITE CHEMISTRY 309
EXPERIMENTAL DATA 311
HYPOTHESES: DIVERGENT PLATES AND THE ORIGIN OF PODIFORM CHROMITE DEPOSITS 313