Peridot is a gem-quality variety of the mineral olivine. It belongs to the forsterite-fayalite mineral series. Some even refer to peridot as ‘olivine’, but when it comes to the gemstone, ‘peridot’ is the correct term. 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. Thus, peridot is found only in green. In fact, peridot is one of the few gemstones available that can be found only in one color, although the shades of green may vary from light yellowish to dark brownish-green.
The name ‘peridot’ was derived from the Arabic word for gem – ‘faridat’. It is sometimes referred to as ‘the poor man’s emerald’ or as ‘chrysolite’, a word derived from the Greek word ‘goldstone’. It is one of the oldest known gemstones, with records dating back as early as 1500 B.C. Historically, the volcanic island of Zabargad (St. John) in the Red Sea, east of Egypt, had the most important deposit that was exploited for over 3500 years. Today, the finest quality peridot comes from Mogok in Burma, although Pakistani peridot is now highly regarded as well. There are other very important deposits found in Arizona, China and Vietnam. Peridot has also been discovered in fallen meteors and it has also been discovered on Mars and the moon in olivine form.
Chemically, peridot is an iron magnesium silicate and its intensity of color depends on the amount of iron it contains. There may also be traces of nickel and chromium present. Peridot is not especially hard and it has no resistance to acid. On very rare occasions, peridot is known to form with cat’s eye chatoyancy (asterism) in the form of four ray stars. Peridot can be mistaken for similar colored gems, but its strong double refraction is often a very distinguishing trait. In thicker stones, the doubling of lower facet edges can be easily seen by looking down through the table without the need for magnification.
Most gemstones are formed in earth’s crust, but peridot is formed much deeper in the mantle region. Peridot crystals form in magma from the upper mantle and are brought to the surface by tectonic or volcanic activity where they are found in extrusive igneous rocks. Historically the volcanic island Zabargad (St. John) in the Red Sea was the location of the most important deposit. It was exploited for 3500 years before it was abandoned for many centuries; later, it was rediscovered around 1900 and has been heavily exploited ever since.
Today, the most important deposits are found in Pakistan (in the Kashmir region and the Pakistan-Afghanistan border region). Beautiful material is also found in upper Myanmar (Burma) and Vietnam. Other deposits are found in Australia (Queensland), Brazil (Minas Gerais), China, Kenya, Mexico, Norway (north of Bergen), South Africa, Sri Lanka, Tanzania and the United States (Arizona and Hawaii). Recently, China has become of the largest producers of peridot.
Peridot is one of the few gemstones that comes in a single color. The depth of green depends on its level of iron content. Peridot’s color can vary from yellow-green and olive to brownish green and looks best under natural daylight. Its vivid green color does not change under artificial light. 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. A deep and intense green colored peridot is considered the most desirable and the most valuable.
Peridot Clarity and Luster
Peridot occurs with excellent transparency. Eye-clean specimens are abundant. Larger stones may appear slightly cloudy owing to the presence of inclusions and impurities. When cut and polished, peridot has an attractive, greasy and vitreous luster.
Peridot Cut and Shape
Peridot is typically faceted due to its excellent transparency. Table and step cuts are very popular, as well as unconventional checkerboards. Peridot can be found in many shapes including fancies and traditional rounds, ovals, emeralds (octagons) and cushions.
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