Peridot (pronunciation: /ˈpɛrɪˌdɒt/, /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 is uncertain, the Oxford English Dictionary suggesting an alteration of Anglo-Norman pedoretés (classical Latin paederot-, paederos), a kind of opal, rather than the Arabic word faridat, meaning "gem". Peridot is one of the few gemstones that comes in only one color. The depth of green depends on how much iron is contained in the crystal structure, and varies from yellow-green to olive to brownish green. Olivine is a very abundant mineral, but gem quality peridot is rather rare. 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..
Peridot olivine with minor pyroxene, on vesicular basalt. (FOV = 60mm)
Peridot from the San Carlos Apache reservation in Arizona.
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