Tanzanite

Color : Sapphire blue, amethyst, violet 
Color of streak: White

Mohsí hardness : 6.5-7
Specific gravity : 3.35   
Cleavage : Perfect 

Fracture: Uneven, brittle 
Crystal system : Orthorhombic
Chemical composition : Calcium aluminium silicate
Refractive index : 1.691-1.700
Double refraction : +0.009 
Flourescence : None


The name tanzanite (after the East African state of Tanzania) was introduced be the New York jewelers Tiffany & Co. It is accepted by the trade, although scientists do not encourage a multitude of names for gemstones and refer to it as blue zoisite. In good quality the color is ultramarine to sapphire blue; in artificial light, more amethyst violet. When heated to 752-932 F / 400-500 C, the yellow and brown tints vanish, and the blue deepens. Tanzanite catís eyes are also found. Some deposits in Tanzania near Arusha occur in veins or filling of fissures of gneisses.