Understanding gemstones in a geological context
Gemstones are colorful treasures of the Earth that have captivated humans for thousands of years. The physical and chemical characteristics of each type of gem provide insights into the geological processes that created them.
Geology and Mineralogy of Gemstones is a textbook aimed at upper-level undergraduate and graduate students. It presents the basic mineralogical and geological knowledge needed to understand gemstones and examines the characteristics and geological origins of different types of gemstone.
Volume highlights include:
- Concepts in mineralogy
- Structure and chemical composition of minerals
- Geological processes that lead to the formation and movement of gemstones
- Equipment and tools used to examine gemstones and their physical properties
The American Geophysical Union promotes discovery in Earth and space science for the benefit of humanity. Its publications disseminate scientific knowledge and provide resources for researchers, students, and professionals.
Table of Contents
Preface xi
Acknowledgements xiii
Part I Developing Base Knowledge 1
1 Minerals and Mineralogy 3
1.1 Minerals and Rocks 3
1.2 What is a Gemstone? 3
1.3 Atoms, Elements, and Bonding 4
1.3.1 Protons, Neutrons, and Electrons 4
1.3.2 Atomic Mass 5
1.3.3 Atomic Structure, Electrical Charges, and Ions 5
1.3.4 Elements 6
1.3.5 Element Groups 6
1.3.6 Elemental Abundance in the Earth’s Crust 7
1.3.7 Compounds and Mixtures 8
1.3.8 Chemical Bonds 8
1.4 Physical Properties of Minerals 9
References 11
2 Basics of Rocks and Geology 13
2.1 Earth System Science 13
2.2 The Earth’s Structure and Plate Tectonics 13
2.3 General Rock Types and the Rock Cycle 19
2.4 Metasomatism and Hydrothermal Fluids 23
2.5 Geological Structures 24
2.6 Important Rock Types for Gemstone Deposits 24
2.7 Weathering, Sedimentation, and Secondary Gem Deposits 26
References 28
3 Intermediate Mineralogy 29
3.1 Structure and Chemistry of Minerals 29
3.1.1 Crystallography and Symmetry 29
3.1.2 Mineral Classes 32
3.1.3 Mineral Formulae 32
3.1.4 Element Substitutions 33
3.2 Light 34
3.2.1 Reflection and Refraction 34
3.2.2 Illumination 39
3.2.3 Dispersion 41
3.2.4 Optic Class 42
3.2.5 Color in Minerals 43
3.2.6 Pleochroism 44
3.2.7 Transparency 46
References 47
4 Concepts of Gemmology and Tools 49
4.1 Concepts of Gemmology 49
4.1.1 Gemmological Properties for Testing, Faceting, and Treatments 49
4.2 Tools 51
4.2.1 Collecting and Field Tools 51
4.2.2 Gemmological Tools 52
4.2.3 Advanced Tools 57
References 60
Part II Gemstones and Their Origins 63
5 Diamond 65
5.1 Introduction 65
5.2 Basic Qualities of Diamond 67
5.2.1 Crystal Structure 68
5.2.2 Crystal Chemistry and Type Classification of Diamond 69
5.2.3 Diamond Crystal Forms 71
5.2.4 Colored Diamonds 74
5.3 Common Diamond Treatments 76
5.4 Synthetic Diamond 79
5.5 Geology of Diamond and Kimberlite 79
5.5.1 Diamond Growth 81
5.5.2 Kimberlite Volcanoes 82
5.5.3 Lamproite 83
5.6 Global Distribution and Production of Diamond 84
5.7 Diamonds from Canada 92
5.8 The 4 Cs 95
5.8.1 Cut 95
5.8.2 Clarity 95
5.8.3 Color 96
5.8.4 Carat 98
5.9 Diamond Shapes 98
5.10 Diamond Valuation 99
5.11 Kimberley Process: A 5th C? 100
References 100
6 Corundum 103
6.1 Introduction 103
6.2 Basic Qualities of Corundum 104
6.2.1 Chemistry and Crystal Structure of Corundum 104
6.2.2 Corundum Crystal Forms 104
6.2.3 Colors of Corundum 104
6.3 Faceted Gem Corundum 107
6.4 Corundum Valuation 107
6.5 Corundum Treatments, Synthetics, and Imitations 110
6.6 Geology of Gem Corundum: Three Main Genetic Models 113
6.6.1 Metamorphic Corundum in Silica-Deficient Gneisses, Mafic-Ultramafic Rocks and Marbles 114
6.6.2 Xenocrysts in Alkali Basalts and Lamprophyres 118
6.6.3 Secondary Accumulation in Placers 120
6.7 Rarity of Gem Corundum 124
6.8 Global Distribution and Production of Corundum 124
References 127
7 Beryl 131
7.1 Introduction 131
7.2 Basic Qualities of Beryl 132
7.2.1 Chemistry and Crystal Structure of Beryl 132
7.2.2 Colors of Beryl and Gem Varieties 134
7.3 Beryl Valuation 138
7.4 Common Treatments, Synthetics, and Imitations 140
7.5 Geology of Gem Beryl: Three Main Genetic Models 141
7.5.1 Pegmatitic 141
7.5.2 Magmatic 141
7.5.3 Metamorphic 146
7.6 Large Beryl Crystals 149
7.7 Global Distribution of Beryl 149
References 150
8 Pegmatites 153
8.1 Introduction 153
8.2 Pegmatite Mineralogy 153
8.3 Pegmatite Genesis 154
8.4 Geochemical Families of Pegmatites 155
8.5 Pegmatite Morphology 157
8.6 Corrosion 161
8.7 Rarity of Gem-Bearing Pegmatites 162
8.8 Tourmaline 162
8.8.1 Introduction and Basic Qualities of Tourmaline 162
8.8.2 Chemistry and Crystal Structure of Tourmaline 165
8.8.3 Colors and Gem Varieties of Tourmaline 166
8.8.4 Tourmaline Recognition, Value and Treatments 168
8.9 Spodumene 172
8.9.1 Introduction and Basic Qualities of Spodumene 172
8.9.2 Colors and Gem Varieties of Spodumene 173
8.9.3 Spodumene Recognition, Value, and Treatments 173
8.10 Topaz 175
8.10.1 Introduction and Basic Qualities of Topaz 175
8.10.2 Geology of Gem Topaz 176
8.10.3 Colors and Gem Varieties of Topaz 179
8.10.4 Topaz Recognition, Value, and Treatments 181
References 181
9 Chrysoberyl 185
9.1 Introduction and Basic Qualities of Chrysoberyl 185
9.2 Geology of Gem Chrysoberyl 185
References 189
10 Spinel 191
10.1 Introduction and Basic Qualities of Spinel 191
10.2 Geology of Gem Spinel 192
References 195
11 Tanzanite 197
11.1 Introduction and Basic Qualities of Tanzanite 197
11.2 Geology of Tanzanite 197
References 200
12 The Garnet Group 201
12.1 Introduction and Basic Qualities of the Garnet Group 201
12.2 Geology of Gem Garnet 201
References 207
13 Jade: Jadeite and Nephrite 209
13.1 Introduction and Basic Qualities of Jade 209
13.2 Geology of Jade 209
References 217
14 Quartz and Silica Gems 219
14.1 Introduction and Basic Qualities of Quartz and Silica Gem Varieties 219
14.2 Quartz 219
14.3 Amethyst 220
14.4 Agate 221
14.5 Opal 222
References 228
15 Other Gems 231
15.1 Olivine 231
15.1.1 Introduction and Basic Qualities of Olivine 231
15.1.2 Geology of Gem Peridot 231
15.2 Turquoise 236
15.2.1 Introduction and Basic Qualities of Turquoise 236
15.2.2 Geology of Turquoise 237
15.3 Lapis Lazuli 238
15.3.1 Introduction and Basic Qualities of Lapis Lazuli 238
15.3.2 Geology of Lapis Lazuli 238
15.4 Zircon 243
15.4.1 Introduction and Basic Qualities of Zircon 243
15.4.2 Geology of Gem Zircon 244
References 247
16 Organic Gems 251
16.1 Amber 251
16.2 Ammolite 251
References 257
Index 259
