Benitoite
| Benitoite | |
|---|---|
 Benitoite on natrolite |
|
| General | |
| Category | Silicate mineral |
| Chemical formula | BaTiSi3O9 |
| Strunz classification | 9.CA.05 |
| Crystal symmetry | Hexagonal 6 m2 ditrigonal dipyramidal |
| Unit cell | a = 6.641 Å, c = 9.7597(10) Å; Z = 2 |
| Identification | |
| Color | Blue, colorless |
| Crystal habit | Tabular dipyramidal crystals, granular |
| Crystal system | Hexagonal |
| Twinning | On {0001} by rotation |
| Cleavage | [1011] poor |
| Fracture | Conchoidal |
| Mohs scale hardness | 6 - 6.5 |
| Luster | Vitreous |
| Streak | White |
| Diaphaneity | Transparent to translucent |
| Specific gravity | 3.6 |
| Optical properties | Uniaxial (+) |
| Refractive index | nω = 1.756 - 1.757 nε = 1.802 - 1.804 |
| Birefringence | δ = 0.046 |
| Pleochroism | O = colorless; E = purple, indigo, greenish blue |
| Solubility | Insoluble: HCl, H2SO4 Soluble: HF |
| Other characteristics | Blue fluorescence under SW UV; intense blue cathodoluminescence |
| References | [1][2][3] |
Benitoite (ben-EE-toe-ite) 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.[4][5]
Benitoite occurs in a number of sites, but gemstone quality material has only been found in California.[citation needed] It is California's official state gem.
[edit] 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.[3]
In 1985 benitoite was named as the official state gem of California.[6]
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Blue Benitoite Crystals on white natrolite, Dallas Gem Mine, San Benito Co., California, USA
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Benitoite crystals under UV light
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[edit] References
- ^ WebMineral Listing
- ^ MinDat Listing
- ^ a b Handbook of Mineralogy
- ^ Louderback, George Davis. Bentiote, A New California Gen Mineral. Bulletin of The Department of Geology, Vol. 5, No. 9. University of California Publications. July, 1907
- ^ http://www.mineralsocal.org/scfm/newsletters/2002%20march.htm Friends of Mineralogy review of benitoite
- ^ http://www.consrv.ca.gov/cgs/geologic_resources/mineral_resource_mapping/ Mineral Resources California Geologic Survey. Accessed December 31, 2005
