Peridot is a gem-quality variety of olivine. It belongs to the forsterite-fayalite mineral series. Peridot is an idiochromatic gem, meaning its color comes from the basic chemical composition of the mineral itself and not from minor traces of impurities.
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. Peridots can also be found in meteorites.
Olivine, in general, is a very abundant mineral, but gem quality peridot is rather rare. This is due to the mineral's chemical instability on the Earth's surface. Olivine is usually found as small grains and tends to exist in a heavily weathered state, unsuitable for decorative use. Large crystals of forsterite, the variety most often used to cut peridot gems, are rare; as a result olivine is considered to be precious.
Peridot is the official birthstone for the month of August as adopted by the American National Association of Jewelers in 1912. It is also the stone for the Zodiac sign of Libra. Peridot is assigned to the planet Saturn. It may be given as a gem on the sixteenth wedding anniversary.
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. Its vivid green color does not change under artificial light.
Chemically, peridot is a magnesium iron silicate, and its intensity of color depends on the amount of iron it contains. There may also be traces of nickel and chromium present.
The best-colored peridot has an iron percentage of less than 15% and typically includes some trace elements of nickel and chromium, which contribute to its color. The most valued color is a dark olive-green.
Peridot is the gem variety of olivine and ranges between 6.5 and 7 on the Mohs scale of hardness. It is not particularly sensitive to acid, but it does have a brittle tenacity.
The name "Peridot" is believed to have originated from the Arabic word faridat, meaning "gem", or, as the Oxford English Dictionary suggests, it came from classical Latin pæderot - a kind of opal.
The ancient Romans called it 'evening emerald' since its color did not darken at night, but could still be appreciated by candlelight and the light of a campfire.
Peridot is a healing gemstone often associated with peace, compassion, and harmony of relationships. Its powers are thought to promote growth and renewal while alleviating negative emotions such as guilt, resentment, and apathy.
It is a gem especially connected with ancient Egypt, and some historians believe that the famous emeralds of Cleopatra were actually peridot gems.
Peridot olivine is mined in Arkansas, Arizona on the San Carlos Reservation, Hawaii, Nevada, and New Mexico at Kilbourne Hole, in the US; and in Australia, Brazil, China, Egypt, Kenya, Mexico, Myanmar (Burma), Norway, Pakistan, Saudi Arabia, South Africa, Sri Lanka, and Tanzania.
The name chrysolite was formerly applied not only to peridot but also many similarly colored stones.
Even though peridots existed in ancient history, at one point they vanished until some were found 30 years ago in Pakistan.