Benitoite

Infobox mineral
name = Benitoite
category = Mineral
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caption = Benitoite on natrolite
formula = bariumtitaniumsilicon₃ oxygen₉
(barium titanium silicate)
molweight =
color = Blue; Colorless
habit = Tabular dipyramidal crystals, granular
system = Hexagonal
twinning =
cleavage = [1011] Poor
fracture = Conchoidal
mohs = 6 - 6.5
luster = Vitreous
refractive = 1.757-1.759; 1.802-1.804
opticalprop =
birefringence =
pleochroism = Dichroic (blue to white)
streak = White
gravity = 3.6
melt =
fusibility =
diagnostic =
solubility = Insoluble: HCl, H₂SO₄
Soluble: HF
diaphaneity = Transparent to translucent
other =
references = [http://webmineral.com/data/Benitoite.shtml WebMineral Listing] [http://www.mindat.org/min-624.html MinDat Listing]

Benitoite is a rare blue silicate mineral, found in hydrothermally altered serpentinite. Benitoite fluoresces under short wave ultraviolet light, appearing light blue in color. Dr. Louderback, who conducted the discovery examination of this mineral, named it Benitoite, “as it occurs near the head waters of the San Benito River in San Benito County,” California. [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]

Uses of benitoite

Benitoite's rarity makes it a minor ore for barium or titanium at best. Rather, benitoite's main uses are as collector's specimens, especially in specimens which show off this mineral's unique crystals, or specimens in which benitoite occurs with its commonly associated minerals. Benitoite's hardness also makes it suitable for use as a gemstone, though the general lack of usable material has limited this use. When quality material is attained, faceted gemstones are highly valued by collectors, as Benitoite has the color of the finest sapphires combined with the strong dispersion, or "fire", of high quality diamonds.

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:

Benitoite is a rare mineral, found in very few locations, most prominently in southern San Benito County, California, but also in Japan and Arkansas. In the San Benito occurrence it is found in natrolite veins within glaucophane schist within a serpentinite body. In Japan it occurs in a magnesio-riebeckite-quartz-phlogopite-albite dike cutting a serpentinite body. [http://rruff.geo.arizona.edu/doclib/hom/benitoite.pdf Handbook of Mineralogy] Benitoite is typically found with some combination of natrolite, joaquinite, and neptunite on a greenish-grey serpentinite base. Finally, benitoite's fluorescence is used for identification purposes.

Trivia

Benitoite is the official state gem of California. [http://www.consrv.ca.gov/cgs/geologic_resources/mineral_resource_mapping/ Mineral Resources California Geologic Survey. Accessed December 31, 2005]

Benitoite is the official gem of E Clampus Vitus.

References