Tanzanite (Rough)

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.

Identified on: 4/23/2026

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