Category Cyclosilicate Strunz classification 9.CA.05 Space group P6c2 | Formula
(repeating unit) BaTiSi3O9 Crystal system Hexagonal | |
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Crystal class Ditrigonal dipyramidal (6m2)
H-M symbol: (6 m2) | ||
Benitoite ( /bɛn.ˈi.toʊ.aɪt/) is a rare blue barium titanium silicate mineral, found in hydrothermally altered serpentinite. Benitoite fluoresces under short wave ultraviolet light, appearing bright blue to bluish white in color. The more rarely seen clear to white benitoite crystals fluoresce red under long-wave UV light.
It was first described in 1907 by George D. Louderback, who named it benitoite for its occurrence near the headwaters of the San Benito River in San Benito County, California.
Benitoite occurs in a number of sites, but gemstone quality material has only been found in California. In 1985 benitoite was named as the official state gem of California.
Benitiote has a rare 5 pointed crystal form, and an even rarer 6 pointed form, "star of David", with about 24 samples known.
Associated minerals and locations
Benitoite typically occurs with an unusual set of minerals, along with minerals that make up its host rock. Frequently associated minerals include: natrolite, neptunite, joaquinite, serpentine and albite.
Benitoite is a rare mineral found in very few locations including San Benito County, California, Japan and Arkansas. In the San Benito occurrence, it is found in natrolite veins within glaucophane schist within a serpentinite body. In Japan, the mineral occurs in a magnesio-riebeckite-quartz-phlogopite-albite dike cutting a serpentinite body.