Crystal Tanzanite

Chemical Formula

Ca₂Al₃(SiO₄)₃(OH)

Color

Blue, Purple

Hardness

6 - 6.5

Crystal System

Orthorhombic

Refractive Index

1.69 - 1.70

SG

3.2 - 3.4

Transparency

Transparent to translucent

Double Refraction

.009

Luster

Vitreous

Cleavage

1,1

Mineral Class

Zoisite