Table I
Chemical Composition of Gem-Stones
| (a) Elements— | ||
| Diamond | C | |
| (b) Oxides— | ||
| Corundum | Al2O3 | |
| Quartz | SiO2 | |
| Chalcedony | SiO2 | |
| Opal | SiO2.nH2O | |
| (c) Aluminates— | ||
| Spinel | MgAl2O4 | |
| Chrysoberyl | BeAl2O4 | |
| (d) Silicates— | ||
| Phenakite | Be2SiO4 | |
| Dioptase | H2CuSiO4 | |
| Peridot | Mg2SiO4 | |
| Zircon | ZrSiO4 | |
| Enstatite | MgSiO3 | |
| Diopside | CaMg(SiO3)2 | |
| Nephrite | CaMg3(SiO3)4 | |
| Sphene | CaTiSiO5 | |
| Benitoite | BaTiSi3O9 | |
| Andalusite | Al(AlO)SiO4 | |
| Kyanite | (AlO)2SiO3 | |
| Topaz | [Al(F,OH)]2SiO4 | |
| Epidote | Ca2(Al,Fe)2(AlOH)(SiO4)3 | |
| Euclase | Be(AlOH)SiO4 | |
| Prehnite | H2Ca2Al2(SiO4)3 | |
| Iolite | H2(Mg,Fe)4Al8Si10O37 | |
| Garnet { | Hessonite | Ca3Al2(SiO4)3 |
| Pyrope | Mg3Al2(SiO4)3 | |
| Almandine | Fe3Al2(SiO4)3 | |
| Andradite | Ca3Fe2(SiO4)3 | |
| Beryl | Be3Al2(SiO3)6 | |
| Spodumene | LiAl(SiO3)2 | |
| Jadeite | NaAl(SiO3)2 | |
| Moonstone | KAlSi3O8 | |
| Tourmaline | 12SiO2.3B2O3.(9-x)[(Al,Fe)2O3].3x[(Fe, Mn,Ca,Mg,K2,Na2,Li2,H2)O].3H2O | |
| Axinite | HCa3Al2B(SiO4)4 | |
| Idocrase | (Ca,Mn,Mg,Fe)2(Al,Fe)(OH,F)]Si2O7 | |
| (e) Phosphates— | ||
| Beryllonite | NaBePO4 | |
| Apatite | Ca5(F,Cl)(PO4)3 | |
| Turquoise | CuOH.6[Al(OH)2].H5.(PO4)4 | |
Table II
Colour of Gem-Stones
Colourless and White.—Diamond, corundum (white sapphire), topaz, quartz (rock-crystal), zircon (when ‘fired’), moonstone; rarely beryl, tourmaline; among the less common species, phenakite, spodumene (colourless kunzite), beryllonite.
Yellow.—Diamond, topaz, corundum (yellow sapphire), quartz (citrine, Scotch or occidental topaz), tourmaline, zircon, sphene, spodumene, beryl.
Pink and Lilac.—Corundum (pink sapphire), spinel (balas-ruby), tourmaline (rubellite), topaz (usually when ‘fired’), spodumene (kunzite), beryl (morganite), quartz (rose-quartz).
Red.—Corundum (ruby), garnet (pyrope, almandine), spinel (balas-ruby), tourmaline (rubellite), zircon, opal (fire-opal).
Green.—Beryl (emerald, aquamarine), peridot, corundum, tourmaline, chrysoberyl (including alexandrite), zircon, garnet (demantoid); among less common species, spodumene (hiddenite), euclase, diopside, idocrase, epidote, apatite, obsidian; rarely diamond; also semi-opaque, turquoise, jade.
Blue.—Corundum (sapphire), spinel, topaz, tourmaline, zircon; among the less common species, kyanite, iolite, benitoite, apatite; rarely diamond; also semi-opaque, turquoise, lapis lazuli, sodalite.
Violet and Purple.—Quartz (amethyst), corundum (oriental amethyst), spinel (almandine-spinel), garnet (almandine), spodumene (kunzite), apatite.
Brown.—Diamond, tourmaline, quartz (smoky-quartz); among the less common species, andalusite, axinite, sphene.