Tanzanite
Image: Robert M. Lavinsky (CC BY-SA 3.0)
Mineral NameTanzanite
Chemical FormulaCa₂Al₃(SiO₄)₃(OH)
Mohs Hardness6
Crystal Systemorthorhombic
Lustervitreous
Streak Colorwhite
Cleavageperfect on {010}
Fractureuneven to conchoidal
Specific Gravity3.1
Colorsblue, violet, purple, burgundy
Transparencytransparent
Type LocalityMerelani Hills, Arusha Region, Tanzania
Mineral GroupSilicates
Usesjewelry, collector
Associated Mineralsgraphite, diopside, tremolite, quartz, calcite
Rarityrare
Description
Tanzanite is a striking blue-violet to violet-blue gemstone, often exhibiting strong pleochroism, appearing different colors from various angles. It typically forms prismatic crystals, sometimes with striations.
Geological Context
Tanzanite forms in regionally metamorphosed graphitic gneisses and schists, often associated with calcium-rich rocks. Its distinctive color is due to the presence of vanadium, which changes oxidation states upon heating.
