A Guide to Buying Peridot
Peridot is a name used to describe the gem variety of the forsterite to fayalite olivine series. It was originally discovered on the island of Topazos in the Red Sea about 300 B.C. and was named topazion by the Egyptians. The island was eventually renamed Zabargad which is Arabic for peridot, and around the 18th century the British began to refer to it as such. The ideal color of peridot would be the perfect example of grass-green, caused by the ferrous iron which is inherent to its composition. To achieve this ideal color requires about a 10-15% quantity of iron, more or less will result in either a greenish-yellow, yellowish-green or even brown tone. The stone derives its color from its ability to absorb certain light rays (idiochromatic), and is therefore not as susceptible to variances in red and blue light rays, generally looking good in all light.
Because peridot is not a particularly expensive stone, eye clean clarity is expected, and it will be found in a much larger variety of cuts relative to more expensive gems. Ranging from tumbled beads to faceted stones, in the higher quality specimens the focus should be on good cutting, with symmetry and beauty emphasized rather than trying to conserve the material. It is common to find faceted stones in sizes from 0.5 carat to 10 carats or more, however there are some extremely rare faceted stones known to exist of over 300 carats. Due to the isolated location of Zabargad, stones have not been produced from there for decades. Large faceted stones ranging from tens to hundreds of carats from a place in Burma’s Mogok Stone Tract called Pyaung Gaung are generally considered to be the best, although a deposit found more recently in the Suppatt region of Pakistan are of comparable quality. It has also been found in Australia, Brazil, China, Norway, and the United States. Stones from the San Carlos Apache Indian Reservation in the U.S are considered to be high quality but rarely found in gems larger than 10 carats. Peridot is typically not enhanced, and has never been grown synthetically although imitations do exist. Tourmaline is commonly used as a natural imitation, green-glass the most prevalent man-made, although it is easily detectable due to the single refractive nature of glass. Well cut peridot ranges from about $50-$80 per carat for stones in the 1-2 carat range, all the way up to $400-$450 per carat for large gems of excellent color.
Properties of Peridot Composition | Peridot is the gem variety of the olivine group, which has the following species:
Forsterite – Mg2SiO4
Fayalite – Fe2SiO4 | Refractive Index | 1.654–1.690 (±0.020) | Specific Gravity | 3.34 + 0.17, – 0.07 | Hardness (Mohs) | 6.5 to 7 | Crystal System | Orthorhombic; usually occurs as rounded pebbles; well formed crystals are quite rare. | Pleochroism | Weak to moderate, dichroic | Birefringence | 0.035 to 0.038 | Optic Character | Biaxial (positive or negative; the beta index is usually near halfway between alpha and gamma) | Dispersion | 0.020 | UV Fluorescence | Generally inert | Phenomena | Cat's eye and star peridot are known but rare | Cleavage | Imperfect to distinct in one direction (rarely seen) | Colors | Mainly green; sometimes yellow or brown | Enhancements | Not typically enhanced. | Handling | Avoid exposure to heat, acids and rapid temperature changes. Steamer: not safe Ultrasonic: not safe; never clean peridot ultrasonically
The best way to care for peridot is to clean it with warm soapy water. | Synthetic available? | No |
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