What is Benitoite?
Benitoite 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 colour. The more rarely seen clear to white benitoite crystals fluoresce red under long-wave UV light.
California designated benitoite as the official state gemstone in 1985. Benitoite is sometimes called the "blue diamond." First discovered near the headwaters of the San Benito River in 1907 (hence the name), benitoite is a very rare gem that ranges in colour from a light transparent blue to dark, sapphire blue, or occasionally a violet shade.
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| Benitoite Crystal. |
Benitoite (pronounced "ben-ee-toe-ite") was initially thought to be a sapphire, but after careful analysis was found to be a mineral new to science. Gem quality benitoite cyrstals are found only in California.
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.
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| Benitoite Crystal under UV. |
Physical Properties of Benitoite
| Chemical Formula | BaTiSi3O9 |
| Colour | Blue |
| Hardness | 6 - 6.5 |
| Crystal System | Hexagonal |
| Refractive Index | 1.75 - 1.80 |
| SG | 3.6 |
| Transparency | Transparent |
| Double Refraction | 0.047 |
| Luster | Vitreous |
| Cleavage | 3,1 |
| Mineral Class | Benitoite |