Benitoite is the rare barium-titanium cyclosilicate that became California’s state gem in 1985. Its sapphire-blue triangular dipyramidal crystals from a single deposit in San Benito County are unmistakable, and the species is essentially restricted to that locality in gem grade.
Properties
- Formula: BaTi(Si3O9)
- Crystal system: Hexagonal (ditrigonal-dipyramidal)
- Hardness: 6 – 6.5
- Color: Sapphire-blue, sometimes colorless or pink
- Streak: White
- Luster: Vitreous
- Cleavage: Indistinct on {1011}
- Density: 3.6 g/cm³
Occurrence
The Benitoite Gem Mine (Dallas Gem Mine), San Benito County, California, is the only commercial source — a serpentinite-hosted hydrothermal occurrence with benitoite, neptunite, joaquinite and natrolite. The mine ceased production in 2005, making material increasingly scarce.
Identification
Sapphire-blue triangular dipyramids + brilliant blue-white SW UV fluorescence + association with neptunite (black) and natrolite (white) on serpentine matrix. Distinguish from sapphire (corundum) by hexagonal habit and softness.
Collector Notes
Premier American collector gem; supply has dwindled since the mine closure. Faceted gem benitoite has the highest fire (dispersion) of any common gem species except diamond.
Found at these Localities
- Benitoite Gem Mine (蓝锥矿宝石矿)
