mineral

Tanzanite

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

Hardness: 6.5-7 Mohs; Color: blueish-purple to violet-blue; Luster: Vitreous; Crystal system: Orthorhombic; Cleavage: Perfect in one direction; Specific Gravity: 3.35

Hardness: 6
Color: blueish-purple to violet-blue
Luster: Vitreous

Identified March 13, 2026More mineral →

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Physical properties

Hardness: 6.5-7 Mohs; Color: blueish-purple to violet-blue; Luster: Vitreous; Crystal system: Orthorhombic; Cleavage: Perfect in one direction; Specific Gravity: 3.35

Formation & geological history

Formed by regional metamorphism of calcium-rich igneous rocks; approximately 585 million years old (Late Neoproterozoic/Cambrian period). Found exclusively in a small 4km by 2km area in Tanzania.

Uses & applications

Primary use is in fine jewelry (rings, pendants, earrings) due to its striking color and rarity; it is also a highly sought-after specimen for gem collectors.

Geological facts

It is 1,000 times rarer than a diamond and is famous for its strong pleochroism, showing different colors (blue, purple, and burgundy) when viewed from different angles. It was discovered and named by Tiffany & Co. in 1967.

Field identification & locations

Identify in the field by its distinct trichroic properties (viewing through a dichroscope) and its presence in graphite and kyanite-bearing metamorphic rocks. Locations: Only found in the Mererani Hills of Manyara Region, Tanzania.