Peridot

Infobox mineral
name = Peridot
category = Mineral
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caption =
formula = (Mg, Fe)₂SiO₄
molweight =
color = Yellow, to yellow-green, olive-green, to brownish
habit =
system = Orthorhombic
twinning =
cleavage = Poor
fracture = Conchoidal
mohs = 6.5-7
luster = Vitreous (glassy)
refractive = 1.64-1.70
opticalprop =
birefringence = +0.036
pleochroism =
streak = White
gravity = 3.2-4.3
melt =
fusibility =
diagnostic =
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Peridot (pronunciation: , /ˈpɛrɪˌdoʊ/ (British English), /ˈpɛərɪˌdɑt/, /ˈpɛərɪˌdɑʊ/ (US English)) is the gem quality variety of forsteritic olivine. The chemical composition of peridot is (Mg, Fe)₂SiO₄, with Mg in greater quantities than Fe.

The origin of the name "peridot" is uncertain. The "Oxford English Dictionary" suggests an alteration of Anglo-Norman "pedoretés" (classical Latin "paederot"-), a kind of opal, rather than the Arabic word "faridat", meaning "gem".

Olivine in general is a very abundant mineral, but gem quality peridot is rather rare.

Peridot is one of the few gemstones that occur in only one color: basically an olive green. The intensity and tint of the green however depends on how much iron is contained in the crystal structure, so the color of individual peridot gems can vary from yellow-green through olive green to brownish green.

Peridot crystals have been collected from some Pallasite meteorites.

Peridot olivine is the birthstone for August.

Occurrence

Olivine, of which peridot is a type, is a common mineral in mafic and ultramafic rocks, and it is often found in lavas and in peridotite xenoliths of the mantle, which lavas carry to the surface; but gem quality peridot only occurs in a fraction of these settings.

Peridot olivine is mined in North Carolina, Arizona, Hawaii, Nevada, and New Mexico, in the US; and in Australia, Brazil, China, Kenya, Mexico, Myanmar (Burma), Norway, Pakistan, South Africa, Sri Lanka, and Tanzania. High quality peridot olivine is mined in the eastern lava fields of Saudi Arabia.

The largest cut peridot olivine is a 310 carat (62 g) specimen in the Smithsonian Museum in Washington, D.C..

External links

* [http://mineral.galleries.com/minerals/gemstone/peridot/peridot.htm Mineral Galleries - Peridot]
* [http://www.gemstone.org/gem-by-gem/english/peridot.html Gemstone.org Peridot]
* [http://minerals.usgs.gov/minerals/pubs/commodity/gemstones/sp14-95/peridot.html USGS peridot data]
* [http://www.emporia.edu/earthsci/amber/go340/peridot.htm Emporia Edu]
* [http://micro.magnet.fsu.edu/birthstones/pages/peridot.html Florida State U. - Peridot]