mineral

Tanzanite

Blue/Violet Variety of Zoisite (Ca2Al3(SiO4)3(OH))

AI-generated identification · may be incorrect

Hardness: 6.5-7.0 (Mohs scale); Color: Blue to violet, highly pleochroic; Luster: Vitreous (glassy); Crystal Structure: Orthorhombic; Cleavage: Perfect in one direction; Specific Gravity: 3.35

Hardness: 6
Color: Blue to violet, highly pleochroic
Luster: Vitreous (glassy)

Identified March 13, 2026More mineral →

Explore Tanzanite in the encyclopedia →

Identify your own rocks.

Get a report just like this from any photo, free.

App Store Google Play

Physical properties

Hardness: 6.5-7.0 (Mohs scale); Color: Blue to violet, highly pleochroic; Luster: Vitreous (glassy); Crystal Structure: Orthorhombic; Cleavage: Perfect in one direction; Specific Gravity: 3.35

Formation & geological history

Formed through regional metamorphism. The crystals were created about 585 million years ago during the Pan-African event, involving high heat and pressure within tectonic plate collisions.

Uses & applications

Primarily used as a gemstone in high-end jewelry (rings, pendants, earrings). It is a popular birthstone for December.

Geological facts

Tanzanite is 1,000 times rarer than diamonds because it is found in only one place on Earth: a 4km strip near Mount Kilimanjaro. It was famously discovered and named by Tiffany & Co. in 1968.

Field identification & locations

Identify by its intense trichroism (showing blue, violet, and burgundy from different angles). In the field, look for graphite-rich schists in the Merelani Hills of Tanzania. Collectors look for deep saturation and clarity.