Peridot
| Peridot | |
|---|---|
 | |
| General | |
| Category | Mineral |
| Formula | (Mg, Fe)2SiO4 |
| Crystal system | Orthorhombic |
| Identification | |
| Color | Yellow to yellow-green |
| Cleavage | Poor |
| Fracture | Conchoidal |
| Mohs scale hardness | 6.5-7 |
| Luster | Vitreous (glassy) |
| Streak | White |
| Specific gravity | 3.2-4.3 |
| Refractive index | 1.64-1.70 |
| Birefringence | +0.036 |
Peridot (pronounced "pair-uh-dot" or "pair-uh-doe", IPA: /pɛɹɪdɑt/ or Fr. /peʁido/) 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 name of the gemstone is believed to come from either the Arabic word faridat meaning "gem" or the French word peritot meaning "unclear." 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. Peridot is also often referred to as "poor man's emerald". Olivine is a very abundant mineral, but gem-quality peridot is rather rare. Peridot crystals have been collected from iron-nickel meteorites.
Occurrence
Olivine/peridot is a common mineral in mafic and ultramafic rocks, and is often found in lavas and in peridotite xenoliths of the mantle that lavas carry to the surface; however, 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. Peridot/olivine of high quality is commercially 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.. A special variety of a peridot/olivine from Pakistan is known as "Kashmir" peridot. Due to the large size of the rough stones found there, cutters have successfully created faceted stones of over 100 carats (20 g) from the rough gems of this area.[citation needed]
Peridot/olivine is the birthstone of August.
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