Characteristics of Dumortierite:

Chemical Name: Aluminum-iron borosilicate

Formula: Al₇BO₃(SiO₄)₃O₃

Colors: Blue, violet, brown, green

Structure: Orthorhombic

Hardness: 7-8.5

Specific Gravity: 3.2-3.4

Refractive Index: 1.68-1.69

Lustre: Vitreous

Streak: White

Locations: USA, Madagascar, Japan, Canada, Sri Lanka, South Africa, Italy

What is Dumortierite? 

The most prized colors of Dumortierite are an intense deep blue to violet. Although sometimes found in small crystals, it is best known in its massive form, when it is used for gemstones cut en cabochon, and in carvings. Crystals show pleochroism from red to blue to violet, and have, on rare occasions, been faceted for collectors. Dumortierite occurs in pegmatites, in aluminum-rich metamorphic rocks, and in rocks metamorphosed by boron-bearing vapor from intruding bodies of granite.