Dumortierite

Dumortierite is a minor blue gemstone that usually forms as inclusions in Quartz. Its most common color is blue or grayish-blue, though pink and purple colors are also known. Dumortierite"s durability, combined with a high hardness, would make this an ideal gemstone, but the lack of transparency and often dull luster limit its use. 

Chemical Formula	AlAl6O3BSi3O18
Color	Blue, Pink, Purple
Hardness	7
Crystal System	Orthorhombic
Refractive Index	1.67Â -Â 1.72
SG	3.3Â -Â 3.4
Transparency	Translucent to opaque
Double Refraction	0.01 - 0.04
Luster	Vitreous, silky
Cleavage	2,1;3,1
Mineral Class	Dumortierite