Chemical composition -- Barium titanium silicate.
Color -- blue or purplish blue.
Optics -- R.I 1.76-1.80.
Durability -- Hardness 6-6.5. A little soft for rings, but excellent for earrings, pins, and pendants.
Crystal structure -- Hexagonal.
Specific Gravity -- 3.64-3.68.
Sources -- The only known source of gem quality benitoite is San Benito County, California. Faceted stones are usually under 1 carat; the largest known weighs 7.8 carats and is in the collection of the Smithsonian Institution.
One of the finest and rarest of gemstones, benitoite combines the color of fine blue sapphire with the dispersion of diamond.