Peridot (the origin of the name uncertain, early references to the stone have been made in the Middle English dictionary between 1300 -1500 and by the French in 1667) is the magnesium-rich variety of the silicate mineral Olivine.
Peridot is one of the few gemstones that occur in only one colour, an olive green. However, the intensity and tint of the green depends on how much iron is contained in the crystal structure, so the colour of individual peridot gems can vary from yellow- to olive- to brownish green. The most valued colour is a dark olive green.
Olivine is a common mineral in mafic and ultramafic rocks and is a very abundant mineral in general. However, gem quality peridot is rather rare, the mineral is precious.
It is often found in lava and in the mantle, which lava carries to the surface, but quality peridot only occurs in a fraction of these settings. Peridot can also be found in meteorites. A famous Pallasite meteorite, from which peridot crystals were collected from, was offered for auction in April 2008 with a requested price of close to $3 million at Bonhams, but remained unsold.
Peridot olivine is mined in Egypt, North Carolina, Arizona, Hawaii, Nevada and New Mexico. It is also found in Australia, Brazil, China, Kenya, Myanmar (Burma), Norway, Pakistan, Saudi Arabia, South Africa, Sri Lanka and Tanzania. The largest cut peridot is a 310 carat (62g) specimen in the Smithsonian Museum in Washington D.C. Peridot is the birthstone for the month of August.