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