Chemical composition -- Hydrated aluminum oxide plus manganese.
Color -- Colorless, light shades of pink, yellow, green, brown, or light to dark red (darker red with higher manganese content). Some color change stones have been seen.
Optics -- R.I. 1.70-1.75. Birefringence 0.048. Biaxial positive.
Durability -- Hardness 6.5-7.0. One direction of perfect cleavage, but not so fragile as to preclude cutting or use in protective jewelry.
Crystal structure --Orthorhombic.
Specific Gravity -- 3.3-3.5.
Sources -- Quite rare, outside of some large brownish crystals from Turkey. Recently (Gems & Gemology, Winter 1994), a deposit in Turkey began producing stones with a color change from brownish pink (under incandescent light) to brownish green (under fluorescent light). In recent months, stones showing other color changes have appeared, and supplies are said to be promising.