Benitoite

Chemistry: Barium titanium silicate
Crystal system: Trigonal; crystal class ditrigonal bipyramidal; commonly as trigonal bipyramids.
Color: Transparent to translucent; blue (most common), violet blue, colorless, pink (rare).
Hardness: 6.5
Cleavage: None; Fracture: conchoidal.
Specific gravity: 3.65
Refractive index: 1.75 – 1.80; Uniaxial positive; 0.047; strong doubling.
Luster: Vitreous – sub-adamantine.
Dispersion: High (masked by body color).
Dichroism: Strong (blue and colorless).
Occurrence: San Benito County, California, U.S.A.

Notes
Discovered in 1906; Collectors stone; Looks like sapphire, but pronounced DR, dichroism and high dispersion, luminescence, and lower SG help in separation; bright blue in short wave; faceted, usually round brilliants to display dispersion.