mineral

Tanzanite (Rough)

Blue Zoisite (Ca2Al3(SiO4)3(OH))

Hardness: 6.5-7 (Mohs); Color: Violet-blue to deep blue; Luster: Vitreous; Crystal Structure: Orthorhombic; Cleavage: One perfect direction; Specific Gravity: 3.35

Hardness: 6
Color: Violet-blue to deep blue
Luster: Vitreous

Identified April 23, 2026More mineral →

Identify your own rocks.

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

App Store Google Play

Physical properties

Hardness: 6.5-7 (Mohs); Color: Violet-blue to deep blue; Luster: Vitreous; Crystal Structure: Orthorhombic; Cleavage: One perfect direction; Specific Gravity: 3.35

Formation & geological history

Formed through regional metamorphism. High-pressure, low-temperature metamorphism of basaltic rocks created these blue crystals roughly 585 million years ago during the Pan-African orogenic event.

Uses & applications

Primarily used in high-end jewelry and collected as a rare mineral specimen. It is the birthstone for December.

Geological facts

Tanzanite is one of the rarest gemstones on Earth, found only in a small four-kilometer strip of land near the Merelani Hills of Tanzania. It is approximately 1,000 times rarer than diamonds.

Field identification & locations

Identified by its signature trichroism (showing blue, violet, and burgundy from different angles). In the field, look for the unique intense blue-violet hue in the Merelani mining district. It can be distinguished from sapphire by its lower hardness and specific gravity.