mineral

Tanzanite

Blue Zoisite (Ca2Al3(SiO4)(Si2O7)O(OH))

Hardness: 6.5-7.0 (Mohs); Color: Violet-blue to blue-violet; Luster: Vitreous; Crystal Structure: Orthorhombic; Cleavage: Perfect one direction; Specific Gravity: 3.35

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

Identified April 14, 2026More mineral →

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Physical properties

Hardness: 6.5-7.0 (Mohs); Color: Violet-blue to blue-violet; Luster: Vitreous; Crystal Structure: Orthorhombic; Cleavage: Perfect one direction; Specific Gravity: 3.35

Formation & geological history

Formed in regional metamorphic environments approximately 585 million years ago by extreme heat and pressure in the Mererani Hills. It involves the interaction of calcium-rich pegmatites and schist.

Uses & applications

Predominantly used as a gemstone for high-end jewelry (rings, necklaces, 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 by 2km area in Tanzania. It is famous for its strong trichroism, showing blue, violet, and burgundy colors from different angles.

Field identification & locations

Identify by its unique pleochroism and heat sensitivity. In the field, look for graphite and garnet-rich schist formations near the Kilimanjaro region in Tanzania. It is the only gemstone on the market that is geographically restricted to a single mine location.