Gem-Stones and Their Distinctive Characters

by George Frederick Herbert Smith

Anatase

This mineral, which is one of the three crystallized forms of titanium oxide, TiO₂, occurs often in small, brown, transparent stones which occasionally find their way into the market. The lustre is adamantine. The refraction is uniaxial in character and negative in sign, the extraordinary index being 2·493 and ordinary 2·554. The specific gravity varies from 3·82 to 3·95, and the hardness is about 5½ to 6 on Mohs’s scale.