Table of contents for Gemmology / P.G. Read.


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1  Introduction                                                        1
The evolution of the science of gemmology                           1
Highlights of the last 170 years                                    1
The essential qualities of a gem material                           9
Organic and inorganic gems                                         10
2  The geological origin, occurrence and locality of gemstones     11
The Earth's structure                                              11
Minerals and rocks                                                 12
The formation of rocks in the Earth's crust                        12
Mineral groups, species and varieties                              13
The origin of gems                                                 13
Gem occurrences                                                    16
The major gem localities                                           16
Mining techniques                                                  18
3  The chemical composition of gemstones                           22
Atoms, elements, molecules and compounds                           22
Valency                                                            24
Bonding                                                            25
The relationship between chemical composition and durability       27
4  Crystallography                                                 29
Crystalline and non-crystalline materials                          29
The atomic structure of a crystal                                  31
Classification of crystals by symmetry                             33
The seven crystal systems and their elements of symmetry           34
Crystal forms                                                      38
Crystal habits and their use in identification                     39
Twinned crystals                                                   40
Polycrystalline and microcrystalline minerals                      42
Metamict minerals                                                  42
5  Cleavage, parting and fracture                                  43
The mechanism of cleavage                                        43
Lapidary problems caused by cleavage planes                      44
The use of cleavage in the fashioning of diamond                 46
Parting (false or pseudo-cleavage)                               46
Fracture and its use as an aid to identification                 46
6  Hardness                                                      48
The durability of a gemstone                                     48
Mohs' scale of comparative hardness                              49
Hardness tests (using hardness pencils and plates)               49
Directional hardness                                             51
Engineering hardness tests                                       52
The influence of hardness on mining techniques                   53
7  Specific gravity, density and relative density                54
Definitions                                                      54
Archimedes' principle and the measurement of SG                  54
Measurement of SG by displacement                                55
Hydrostatic methods of SG measurement                            57
Approximation of SG using heavy liquids                          61
Precise measurement of SG using heavy liquids                    65
Sodium polytungstate                                             65
Safety precautions                                               66
8  Colour, lustre and sheen                                      67
The electromagnetic spectrum                                     67
The photon                                                       68
Colour and selective absorption                                  69
Allochromatic and idiochromatic gems                             70
The transition elements                                          70
Colour-change gemstones                                          71
Interference colours                                             72
Dispersion                                                       72
Colour centres                                                   73
Lustre                                                           74
Sheen                                                            74
Colour, transparency and identification                          77
9  Reflection and refraction                                     79
Snell's laws of reflection and refraction                        79
Refractive index                                                 80
Double refraction                                                81
The refractometer                                                82
Contact fluid                                                    84
Sources of illumination                                          84
Using the refractomnter                                          85
The Dialdex refractometer                                        88
Optic axes, optic sign and optical character                     88
Distant vision method                                            91
Special refractometer versions                                   92
Fresnel's reflectivity equation                                  93
The reflectance meter                                            94
Other methods of RI measurement                                  97
10 Polarization and pleochroism                                 105
The polarization of light                                       105
Polarizing filters                                              105
The polariscope                                                 107
Using the polariscope                                           109
Pleochroism (differential selective absorption)                 111
The dichroscope                                                 112
11 Spectroscopy                                                 115
Absorption and emission spectra                                 115
The prism spectroscope                                          116
The diffraction grating spectroscope                            119
Using the spectroscope                                          120
Fine line spectra                                               123
Fraunhofer lines                                                124
Other spectroscope versions                                     125
Raman spectroscopy                                              125
Spectrophotometers                                              126
12 Luminescent, electrical and thermal properties of gemstones  127
Luminescence (fluorescence and phosphorescence)                 127
Photoluminescence and Stokes' law                               128
Crossed filters                                                 128
LW and SW UV radiation                                          130
X-ray radiation                                                 132
Other forms of luminescence                                     133
SW UV transmission test                                         134
Near-UV transparency tester                                     135
Electrical properties                                           135
Thermal conductivity and thermal inertia                        137
Thermal conductance testers                                     138
13 The hand lens, microscope and Chelsea filter                 141
Types of hand lens                                              141
Types of microscope                                             143
Light-field, dark-field and incident illumination               145
Pin-point illumination and shadowing techniques                 147
Immersion techniques                                            147
Additional uses for the microscope                              148
Care in the use of the microscope                               150
The Chelsea filter                                              151
Handling gemstones                                              152
14 Gemstone enhancement                                         155
Foils, colour backing and dyeing                                 155
Impregnation                                                    156
Heat treatments                                                  157
Surface diffusion of corundum                                    160
Lattice diffusion of corundum                                    161
HPHT enhancement of diamond                                      162
Irradiation methods                                              162
Glass filling                                                    165
Laser drilling of diamond                                        166
Disclosure of enhancements                                       167
15 Synthetic gemstones and gemstone simulants                    168
A brief history of early gemstone synthesis                      168
Definitions                                                      169
The Verneuil flame-fusion process                                169
The Czochralski method                                           172
Flux-melt growth                                                 173
Zone melting                                                     176
The hydrothermal process                                         176
The skull-crucible process                                       179
Diamond synthesis                                                181
Thin diamond films                                               184
Chemical vapour deposition (CVD)                                 184
Synthetic jadeite                                                185
'Synthetic' lapis lazuli, turquoise and opal                     185
Composite gemstones                                              186
16 Identifying inorganic gemstones and their synthetic counterparts  189
Growth lines and colour zoning                                   189
Twinning                                                         189
Types of inclusion                                               190
Identification features of natural and synthetic gemstones       190
Colour zone diffusion and induced feathers/fingerprints          204
Use of the polariscope (identifying synthetic quartz and Verneuil corundum) 204
Laboratory equipment and methods                                 205
17 Identifying inorganic gemstone simulants                         212
Alexandrite                                                     -213
Aquamarine                                                       213
Diamond                                                          214
Additional tests for diamond                                     215
Emerald                                                          218
Jade                                                             218
Lapis lazuli                                                     219
Turquoise                                                        219
Opal                                                             220
Quartz                                                           221
Ruby                                                           221
Sapphire                                                       222
18 Identifying organic gem materials and their simulants          223
Natural pearls                                                 223
Cultured pearls                                                225
Distinguishing natural from cultured pearls                    228
Imitation pearls and their identification                      231
Shell                                                          234
Amber                                                          235
Ivory                                                          237
Ondontolite                                                    239
Tortoiseshell                                                  239
Jet                                                            240
Coral                                                          241
19 The fashioning of gemstones                                    243
Critical angle                                                 243
Critical angle and the jewellery owner                         246
Cutting styles                                                 246
Gemstone polishing                                             252
Lapidary techniques                                            252
Gemstone carving                                               254
Diamond polishing methods                                      256
Diamond grading                                                259
20 Practical gemstone identification                              263
Observation                                                    264
Selecting the appropriate tests                                265



Library of Congress subject headings for this publication: Precious stones, Gems