Benitoite (barium titano-silicate)
Color: Ranges from deep blue to colorless. Pink is very rare.
Moh’s hardness: 6-6..5
Refractive index: 1.757-1.804
Critical angle: 34.5°
Specific gravity: 3.65-3.68
Fracture: Conchoidal, brittle.
Dispersion: Strong to very strong (.039 & .046).
Heat sensitivity: None
Pleochroism: Dichroic - Very strong (colorless to blue or green).
Birefringence (double refraction): Strong (.047)
Crystal structure: Trigonal, bipyramidal.
Polishing: Polishing may be problematic. Use alumina or cerium oxide on standard polishing laps.
Comments: With one exception, benitoite is only found in San Benito County in California. There is only one other occurrence, which is a small deposit in Santa Cruz County, California.