mineral

Tanzanite

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

Hardness: 6.5-7.0 (Mohs scale), Color: Vivid blue to violet-blue with trichroism, Luster: Vitreous (glassy), Crystal Structure: Orthorhombic, Cleavage: Perfect in one direction, Specific Gravity: 3.35

Hardness: 6

Identified March 10, 2026More mineral →

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Physical properties

Formation & geological history

Formed in regional metamorphic environments within graphite-bearing schists and gneisses about 585 million years ago. Its unique color is caused by the presence of trace amounts of vanadium.

Uses & applications

Primarily used as a high-end gemstone in jewelry (rings, bracelets, necklaces). It is highly prized by collectors due to its rarity and single-source location.

Geological facts

Tanzanite is 1,000 times rarer than diamonds. It was discovered as recently as 1967 and was named by Tiffany & Co. It is the birthstone for December.

Field identification & locations

Found only in a 4km by 2km area near Mount Kilimanjaro in Tanzania. In the field, it is identified by its strong pleochroism (appearing different colors from different angles) and its distinct violet-blue hue after heat treatment.