Composition: Ca2(OH)Al3(SiO4)3
crystal System:  Orthorombic
Habit: Prismatic (vertically striated) and massive
Refractive Index: 1.69-1.70
Double Refraction and Optic Sign: 0.009  negative
Dispersion: Low (0.012)
Specific Gravity: 3.35
Hardness:  6.5
Cleavage: Perfect-prismatic
Fracture: Uneven
Lustre:  Vitreous
Pleochroism: Strong in blue
Absorption Spectrum: a broad band in the yellow-green and two fainter bamds, one in the green at 528nm and one in the blue at 455nm
Inclusions:
Occurrence:  Tanzania (Blue Zoisite), Norway, Australia and Sourh Africa (Thulite)

Tanzanite