Peridot Buying Guide
PERIDOT BUYING GUIDE
Peridot is one of the prettiest of all green gems, occurring in a color that is the epitome of grass green. Interestingly enough, the name topaz may have initially been applied to peridot, for it is found on the island of Topazos (Zabargad) in the Red Sea.
The name peridot is used to describe the gem variety of the forsterite to fayalite olivine series.
Peridot is ideochromatic, being colored by the ferrous iron that is basic to its composition. The ideal color is a rich grass-green, but some peridot is yellowish green, greenish yellow or brown. The best colors of peridot generally contain about 10–15% of iron.
Peridot is not as light dependent as red and blue gems. It tends to look good under all lights.
Since peridot is not a particularly expensive stone, eye-clean clarity is the standard. Burmese gems are often marred by small platelet inclusions, which may give some stones a sleepy appearance. The strong birefringence (0.036) of peridot can also give stones a slightly sleepy look. This is most pronounced in large stones (10 cts. plus).
Only imagination limits the cuts and shapes applied to peridot, with everything from stunning fantasy cuts to tumbled beads being seen. Again, because it is not terribly expensive, cutters can focus on beauty more than weight retention. This means that good cutting, proportions and symmetry are to be expected. Stay away from misshapen native cut gems, unless they are cheap enough to recut to good proportions.
Peridot ranges in price from about $50–80/ct. for well-cut gems in the 1–2 ct. size, up to as much as $400–450 ct. for large fine gems of top color.
Peridot is common in sizes ranging from melee to faceted stones of 10 cts. or more. Fine faceted stones of greater than 300 carats are known, but quite rare.
Gem peridot has been found in a handful of places around the world. In large sizes (10 cts. plus), Pyaung Gaung in Burma’s Mogok Stone Tract is most important. Faceted gems of hundreds of carats are known from this deposit. In the 1990s, a new deposit from Pakistan’s Suppatt region was discovered, and this material is every bit the equal of that from Burma.
In the US, the San Carlos Apache Indian Reservation supplies good material, but this rarely cuts gems above 10 cts. Peridot is also mined in China, Brazil, Australia and Norway, among other places. The historic deposit of Zabargad has not produced at all in decades.
Peridot is not typically enhanced.
Peridot has never been synthesized, but a number of imitations exist, including natural stones such as tourmaline, and man-made imitations such as glass. Green glass is the most common imitation, and can be easily separated by its single refraction.
Properties of Peridot
|Composition||Peridot is the gem variety of the olivine group, which has the following species:
|Hardness (Mohs)||6.5 to 7|
|Cleavage||Imperfect to distinct in one direction (rarely seen)|
|Specific Gravity||3.34 + 0.17,–0.07|
|Refractive Index||1.654–1.690 (±0.020)|
|Birefringence||0.035 to 0.038|
|Optic Character||Biaxial (positive or negative; the beta index is usually near halfway between alpha and gamma)|
|Crystal System||Orthorhombic; usually occurs as rounded pebbles; well formed crystals are quite rare.|
|Colors||Mainly green; sometimes yellow or brown|
|Pleochroism||Weak to moderate, dichroic|
|UV Fluorescence||Generally inert|
|Phenomena||Cat’s eye and star peridot are known, but are rare|
|Handling||Ultrasonic: not safe; never clean peridot ultrasonically
Steamer: not safe
The best way to care for peridot is to clean it with warm, soapy water. Avoid exposure to heat, acids and rapid temperature changes.
|Enhancements||Peridot is not typically enhanced.|