Chemical composition -- An aluminosilicate of magnesium and iron.
Color -- Blue to violet, showing strong pleochroism. Color orientation in faceted gems is crucial to emphasize the sapphire-like blue coloration, since one direction shows a dingy yellowish-gray color.
Optics -- R.I. 1.52-1.54.
Durability -- Hardness 7-7.5.
Crystal structure -- Orthorhombic.
Specific Gravity -- 2.53-2.78.
Sources -- Major sources include India, Brazil, Sri Lanka (Ceylon).