Crystal Grey Iolite

Chemical Formula

Mg₂Al₄Si₅O₁₈

Color

Blue, Purple, Gray

Hardness

7 - 7.5

Crystal System

Orthorhombic

Refractive Index

1.55 - 1.62

SG

2.6 - 2.7

Transparency

Transparent to translucent

Double Refraction

-0.01

Luster

Vitreous

Cleavage

3,1

Mineral Class

Cordierite