Peridot

For other uses, see Peridot (disambiguation).

Peridot
General
Category	Mineral
Formula (repeating unit)	(Mg, Fe)2SiO4
Crystal system	Orthorhombic
Identification
Color	Yellow, to yellow-green, olive-green, to brownish, sometimes a lime-green, to emerald-ish hue
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 (/ˈpɛrdɒt/ or /ˈpɛrdoʊ/) is gem-quality forsteritic olivine.

Chemistry

The chemical composition of peridot is (Mg, Fe)₂SiO₄, with Mg in greater quantities than Fe. Devin

Etymology

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

Appearance

Peridot is one of the few gemstones that occur in only one color, 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- to olive- to brownish-green. The most valued color is a dark olive-green.

In culture

Peridot olivine is the birthstone for the month of August.

Confusion with other gems

It is sometimes mistaken for emeralds and other green gems. In fact notable gemologist George Frederick Kunz discussed the confusion between emeralds and peridots in many church treasures, notably the "Three Magi" treasure in the Dom of Cologne, Germany.

Occurrence

Geologically

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 can be also found in meteorites.

Abundance

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

Locations of occurrence

Peridot olivine is mined in Egypt, North Carolina, Arizona on the San Carlos Reservation, Hawaii, Nevada, and New Mexico at Kilbourne Hole, in the US; and in Australia, Brazil, China, Kenya, Mexico, Myanmar (Burma), Norway, Pakistan, Saudi Arabia, South Africa, Sri Lanka, and Tanzania. High quality peridot was also recovered from anthills and in lamproite in the Leucite Hills of Wyoming. While searching for diamonds in the Leucite Hills, Dan Hausel recovered 13,000 carats of peridot from two anthills located near the Black Rock lamproite.

In meteorites

Peridot crystals have been collected from some Pallasite meteorites. A famous Pallasite was offered for auction in April 2008 with a requested price of close to $3 million at Bonhams, but remained unsold.

Records

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

Gallery

• 
  Peridot olivine with minor pyroxene, on vesicular basalt. (field of view = 35 mm)
• 
  Peridot from the San Carlos Apache reservation in Arizona.
• 
  Olive Green Peridot
• 
  Peridot with milky inclusions

External links

• Gemstone.org Peridot
• USGS peridot data
• Emporia Edu
• Florida State University – Peridot