Minerology
Peridot (pronounced pair-uh-doh) is a gem variety of olivine (chrysolite) with a transparent lime, olive-green, or yellow-green color. It is composition is a silicate with magnesium and iron impurities. When the ratio of magnesium to iron is very high, the crystal is called forsterite; when it's very low, it's known as fayalite. These two minerals combined form the non-mineral olivine; peridot usually has more forsterite than fayalite, even though fayalite's iron is what produces the green color. (The best peridot is about 15 percent iron.) It has a mineral hardness of 6.5 to 7.
Peridot crystals are formed by the intense heat in volcanoes or, rarely, meteorites, and are found in the resulting igneous rock as flattened crystals, usually only as small grains. The refraction of the crystal is such that light is seen as a split image whenever it passes through, a characteristic which makes peridot easy to identify from impostors such as green garnet or synthetic sapphire and spinel. This unusual refraction gives it a "sleepy" or "fuzzy" appearance, and together with its green color earned it the nickname "evening emerald".
History
Peridot is a French word meaning "unclear", and is derived from the Arabic faridat which simply means "gem". It has been mined as a gemstone for thousands of years. The Old Testament identifies it as "pitdah" and the Israelites probably used it in the breastplates of the high priest. According to legend, peridot was also the favorite gemstone of Cleopatra in ancient Egypt, who may have confused it with emerald. They called it "the gem of the sun" because of its brightness in daylight; it was supposed to be invisible by day and give of its own light at night.
It was mined on Zagbargad Island off the coast of Egypt, also known as St. John's Island, as early as 1500 B.C., according to Pliny. Faceted stones which have been found in the ruins of ancient Greece probably came from the same island. These gems were kept secret from the rest of the world until the seventeenth century, and the mines continued to produce stones all the way through World War II. Peridot was often used to decorate medieval churches, probably carried back to Europe by the Crusaders. Peridots of more than 200 carats adorn the shrine of the three Magi at the Cologne Cathedral.
In the mid-twentieth century, Myanmar became the prime source for peridot with its lighter-green stones, but after the socialist government reduced the supply the San Carlos Apache Reservation in Arizona took over. Today Arizona is still the primary source for peridot worldwide, and a city in that state is named for the gem.
Mythology
Peridot is supposed to bring its wearer success, peace, and good luck, as well as happiness in marriage, freedom from insecurity, and eloquence of speech. Peridot traditionally had the power to dissolve enchantments and drive away evil spirits, a power that was strengthened when the stone was set in gold.
Peridot was also said to strengthen the power of any medicine drunk from goblets carved from the gemstone. As a medical remedy, it was powdered to cure asthma. Holding a peridot under the tongue was supposed to lessen the thirst of a person suffering from fever.
Today
Peridot Mesa, located on the San Carlos Apache Indian Reservation east of Globe in Arizona, is the most productive source of peridot in the world, producing 80 to 95 percent of all stones today. On the Reservation, peridot can be mined only by individual Native Americans or by individual families of Native Americans from the San Carlos Reservation. Other American mineral collectors sometimes gather stones from sources in nearby New Mexico.
Peridot has long been treasured by the natives of Hawaii as tears of the volcano goddess Pele. The island of Oahu even has beaches made from olivine grains. In addition, Pakistan discovered a large deposit of peridot in 1994, yielding one stone of more than 300 carats. Arizona peridots are by far more abundant and affordable, however. Peridot can also be found in Brazil, Germany, Mexico, China, Sri Lanka, Ethiopia, Norway, and Australia.
Peridot is the birthstone for August and is the symbolic gemstone for the 16th wedding anniversary.