PART II—SECTION D

ORGANIC PRODUCTS

XL. PEARL, CORAL, AMBER 291

TABLES

I. CHEMICAL COMPOSITION OF GEM-STONES 300

II. COLOUR OF GEM-STONES 301

III. REFRACTIVE INDICES OF GEM-STONES 302

IV. COLOUR-DISPERSION OF GEM-STONES 303

V. CHARACTER OF THE REFRACTION OF GEM-STONES 303

VI. DICHROISM OF GEM-STONES 304

VII. SPECIFIC GRAVITIES OF GEM-STONES 305

VIII. DEGREES OF HARDNESS OF GEM-STONES 305

IX. DATA 306

INDEX 307

LIST OF PLATES

PAGE I. GEM-STONES (in colour) _Frontispiece_

II. REFRACTIVE INDEX DIAGRAM 36

III. INTERFERENCE FIGURES 48

IV. JEWELLERY DESIGNS 62

V. JEWELLERY DESIGNS 88

VI. APPLIANCES USED FOR POLISHING DIAMONDS 102

VII. POLISHING DIAMONDS 103

VIII. SLITTING AND POLISHING COLOURED STONES 104

IX. FACETING MACHINE 105

X. LAPIDARY’S WORKSHOP AND OFFICE IN ENGLAND 106

XI. LAPIDARY’S WORKSHOP IN RUSSIA 107

XII. FRENCH FAMILY CUTTING STONES 108

XIII. INDIAN LAPIDARY 109

XIV. BLOWPIPE USED FOR THE MANUFACTURE OF RUBIES AND SAPPHIRES 118

XV. KIMBERLEY MINE, 1871 140

XVI. KIMBERLEY MINE, 1872 141

XVII. KIMBERLEY MINE, 1874 142

XVIII. KIMBERLEY MINE, 1881 143

XIX. KIMBERLEY MINE AT THE PRESENT DAY 144

XX. WESSELTON (open) MINE 145

XXI. LOADING THE BLUE GROUND ON THE FLOORS, AND PLOUGHING IT OVER 146

XXII. WASHING-MACHINES FOR CONCENTRATING THE BLUE GROUND 147

XXIII. DIAMOND-SORTING MACHINES 148

XXIV. KAFIRS PICKING OUT DIAMONDS 149

XXV. CULLINAN DIAMOND (natural size) 168

XXVI. LARGE AQUAMARINE CRYSTAL (one-sixth natural size), FOUND AT MARAMBAYA, MINAS GERAES, BRAZIL 196

XXVII. GEM-STONES (in colour) 226

XXVIII. OPAL MINES, WHITE CLIFFS, NEW SOUTH WALES 252

XXIX. GEM-STONES (in colour) 256

XXX. NATIVES DRILLING PEARLS 294

XXXI. METAL FIGURES OF BUDDHA INSERTED IN A PEARL-OYSTER 296

XXXII. SECTIONS OF CULTURE PEARL 297

GEM-STONES