Peridot

Peridot (pronounced pair-a-doe) is the gem variety of olivine. Olivine, which is actually not an official mineral, is composed of two minerals: fayalite and forsterite. Fayalite is the iron rich member with a pure formula of Fe2SiO4. Forsterite is the magnesium rich member with a pure formula of Mg2SiO4. Olivine's formula is written as (Mg, Fe)2SiO4 to show the substitution of the magnesium and iron. Peridot is usually closer to forsterite than fayalite in composition although iron is the coloring agent for peridot. The best colored peridot has an iron percentage of less than 15% and includes nickel and chromium as trace elements that may also contribute to the best peridot color.

Gem quality peridot comes from the ancient source of Zagbargad (Zebirget) Island in the Red Sea off the coast of Egypt; Mogok, Myanmar (formerly known as Burma); Kohistan, Pakistan; Minas Gerais, Brazil; Eifel, Germany; Chihuahua, Mexico; Ethiopia; Australia; Peridot Mesa, San Carlos Apache Reservation, Gila County, Arizona and Salt Lake Crater, Oahu, Hawaii, USA. The best quality peridot has historically come either from Myanmar or Egypt. But new sources in Pakistan are challenging that claim with some exceptional specimens. The Arizona gem material is of lesser quality, but is far more abundant and is therefore much more affordable. An estimated 80 - 95% of all world production of peridot comes from Arizona. The Myanmar, Pakistani and Egyptian gems are rarer and of better quality and thus quite valuable approaching the per carat values of top gemstones. Possibly the most unusual peridot is that which comes from iron-nickel meteorites called pallasites. Some are actually facetted and set in jewelry.

Peridot is perhaps derived from the French word peritot which means unclear, probably due to the inclusions and cloudy nature of large stones. It could also be named from the Arabic word faridat which means gem. In either case, peridot has been mined as a gemstone for an estimated four thousand years or better, and is mentioned in the Bible under the Hebrew name of pitdah. Peridot gems along with other gems were probably used in the fabled Breastplates of the Jewish High Priest, artifacts that have never been found. The Greeks and Romans referred to peridot as topazion and topazius respectively and this name was later given to topaz, to end the confusion with the two gems. Historical legend has it that peridot was the favorite gemstone of Cleopatra. Pliny wrote about the green stone from Zagbargad Island in 1500 B.C.. Even until recently have jewelers used the term "chrysolite" (latin for golden stone) in referring to peridot gems for some reason. This term has also been used to refer to other gemstones, of a more golden color.

Zagbargad (Zebirget) Island has been known as St John's Island and was mined for centuries. Before World War I, this island was extensively mined and produced millions of dollars worth of gems. Since then the mining has been off and on and at present is all but nonexistent. Still, specimens from here are available at times and it certainly is a classic mineral locality.
Throughout time, peridot has been confused with many other gemstones, even emerald. Many "emeralds" of royal treasures have turned out to be peridots! And although peridot is distinctly a different shade of green, many jewelers refer to peridot as "evening emerald". Emerald is a dark green as opposed to a yellow green and always contains inclusions. Other green gemstones confused with peridot include apatite (which is much softer); green garnets (have no double refraction), green tourmaline and green sinhalite (both of which are strongly pleochroic), moldavites (no double refraction) and green zircon (significantly heavier). All of these gemstones rarely have as nice a yellow component to their green color as does most peridot, but darker green peridot can be confusing when good crystal form is not discernible.

Peridot is a beautiful gemstone in its own right and is widely popular. Its popularity is said to be increasing yearly and with new finds in Pakistan producing exceptionally well crystallized specimens, peridot can be fun to collect for years to come.

VARIETY INFORMATION:
VARIETY OF: Olivine , (Mg, Fe)2SiO4.
USES: gemstone.
BIRTHSTONE FOR: August
COLOR: shades of green usually from yellow-green to greenish yellow.
INDEX OF REFRACTION: 1.630 - 1.695
BIREFRINGENCE: 0.037
HARDNESS: 6.5 - 7
CLEAVAGE: usually not discernible
CRYSTAL SYSTEM: orthorhombic