Tanzanite is the trade name for the violet-blue gem variety of zoisite, found at exactly one locality on Earth: the Merelani Hills near Arusha, Tanzania. Discovered in 1967 and marketed worldwide by Tiffany & Co., tanzanite is one of the great gem stories of the late 20th century.
Properties
- Formula: Ca2Al3(SiO4)(Si2O7)O(OH)
- Crystal system: Orthorhombic
- Hardness: 6.5 – 7
- Color: Violet-blue, indigo-blue, often heat-treated from brown
- Streak: White to colorless
- Luster: Vitreous
- Cleavage: Perfect on {010}
- Density: 3.2 – 3.4 g/cm³
Occurrence
Unique locality: Merelani Hills, Manyara Region, Tanzania. Tanzanite forms in graphite-rich pegmatite-hosted gem pockets within metamorphic gneisses of the Mozambique Belt. Most rough is heat-treated (~600°C) to enhance the violet-blue color from natural brown-yellow tones.
Identification
Strong trichroism (blue, violet, brownish-yellow along crystal axes) + Tanzanian pedigree + perfect cleavage. Distinguish from sapphire (harder, no cleavage, isotropic blue) and iolite (lower density, weaker color).
Collector Notes
The Tanzanian government has restricted rough exports since the early 2000s; supply tightening has driven tanzanite into top-tier gem rarity territory. Crystallized rough specimens (uncut crystals on matrix) are increasingly valuable.
Found at these Localities
- Merelani Hills (梅雷拉尼山(坦桑石产地))
