Tanzanite
(tan'-za'-ni-t')
1967; geo. Tanzania
Transparent variety of the mineral zoisite, used as a gem
Color
Light to dark violet to blue
Family
Calcium and aluminum silicate
Chemical composition
Ca2Al3Si3O12OH
Crystal system
Orthorhombic
Hardness (Mohs scale)
6,5 - 7
Specific gravity
3,35 ±0,03
Refractive index
1,691 - 1,700
Optical character
Biaxial +