Benitoite

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Benitoite
Benitoite HD.jpg
Benitoite on natrolite
General
CategoryCyclosilicate
Formula
(repeating unit)
BaTiSi3O9
Strunz classification09.CA.05
Crystal symmetryHexagonal 6 m2 ditrigonal dipyramidal
Unit cella = 6.641 Å, c = 9.7597(10) Å; Z = 2
Identification
ColorBlue, colorless
Crystal habitTabular dipyramidal crystals, granular
Crystal systemHexagonal
TwinningOn {0001} by rotation
Cleavage[1011] poor
FractureConchoidal
Mohs scale hardness6 - 6.5
LusterVitreous
StreakWhite
DiaphaneityTransparent to translucent
Specific gravity3.6
Optical propertiesUniaxial (+)
Refractive indexnω = 1.756 - 1.757 nε = 1.802 - 1.804
Birefringenceδ = 0.046
PleochroismO = colorless; E = purple, indigo, greenish blue
SolubilityInsoluble: HCl, H2SO4
Soluble: HF
Other characteristicsBlue fluorescence under SW UV; intense blue cathodoluminescence
References[1][2][3]
 
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Benitoite
Benitoite HD.jpg
Benitoite on natrolite
General
CategoryCyclosilicate
Formula
(repeating unit)
BaTiSi3O9
Strunz classification09.CA.05
Crystal symmetryHexagonal 6 m2 ditrigonal dipyramidal
Unit cella = 6.641 Å, c = 9.7597(10) Å; Z = 2
Identification
ColorBlue, colorless
Crystal habitTabular dipyramidal crystals, granular
Crystal systemHexagonal
TwinningOn {0001} by rotation
Cleavage[1011] poor
FractureConchoidal
Mohs scale hardness6 - 6.5
LusterVitreous
StreakWhite
DiaphaneityTransparent to translucent
Specific gravity3.6
Optical propertiesUniaxial (+)
Refractive indexnω = 1.756 - 1.757 nε = 1.802 - 1.804
Birefringenceδ = 0.046
PleochroismO = colorless; E = purple, indigo, greenish blue
SolubilityInsoluble: HCl, H2SO4
Soluble: HF
Other characteristicsBlue fluorescence under SW UV; intense blue cathodoluminescence
References[1][2][3]

Benitoite (pronounced /bɛn.ˈi.t.t/) 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. It is California's official state gem.[6]

Benitiote has a rare 5 pointed crystal form, and an even rarer 6 pointed form, "star of David", with about 24 samples known.[7]

Associated minerals and locations[edit]

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.[8]

References[edit]

  1. ^ WebMineral Listing
  2. ^ MinDat Listing
  3. ^ a b Handbook of Mineralogy
  4. ^ 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
  5. ^ http://www.mineralsocal.org/scfm/newsletters/2002%20march.htm Friends of Mineralogy review of benitoite
  6. ^ "Benitoite". Gemology Online. Retrieved 8 November 2012. 
  7. ^ [1]
  8. ^ http://www.consrv.ca.gov/cgs/geologic_resources/mineral_resource_mapping/ Mineral Resources California Geologic Survey. Accessed December 31, 2005