Tanzanite: One Source on Earth — Merelani Hills, Tanzania

Tanzanite (blue-violet zoisite) has never been found in commercial quantities anywhere except the Merelani Hills, Tanzania.

Geological Uniqueness

Formed ~585 Ma during the Pan-African orogeny. Requires a precise cocktail: vanadium + chromium + specific pressure/temperature in graphitic gneiss. The Merelani deposit is a singular geological accident—a 7 km × 2 km block divided into four blocks (A–D).

No Other Sources

• Minor zoisite occurrences exist (Kenya, Norway, Italy, USA, Pakistan), but none yield gem-quality tanzanite color/size.
• Synthetic tanzanite does not exist commercially (unlike sapphire, ruby).
• Treatments: virtually all rough is heated (400–600 °C) to convert brownish trichroic zoisite to blue-violet dichroic tanzanite.

Market Implications

• Single-point supply risk: Mining disruptions (floods, regulation, labor) spike prices.
• Finite resource: Current deep mining (Block C/D, >800 m) extends life ~20–30 years.
• TanzaniteOne (Richland Resources) dominates large-scale; artisanal miners work Block B.

If you own tanzanite, you own a piece of a one-location geological miracle.