Crystal 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