Peridot

History

Peridot, with its captivating apple-green hue, boasts a history stretching back over 4,000 years. The ancient Egyptians held this gem in such high regard that they went to great lengths to keep the location of its volcanic mines a closely guarded secret. The Romans, charmed by its consistent citrus tones, even under candlelight, called it "evening’s emerald". In the Middle Ages, peridot stones were used to adorn cathedrals. This gemstone, the modern August birthstone, has been treasured as a jewellery stone since ancient times. Peridot's particular shade of green depends on its source. The gem is also associated with the 15th wedding anniversary.

Mineral Origins

Peridot is a gem-quality variety of the mineral olivine, belonging to the forsterite-fayalite solid solution series. Forsterite is the magnesium-dominant end, while fayalite is the iron-dominant end. Peridot is found in lava, meteorites, and deep within the Earth’s mantle. It's found in peridotite rock from the earth’s upper mantle. Some peridot is ancient, found in pallasite meteorites, remnants of our solar system's birth. In 2005, peridot was even discovered in comet dust brought back from the Stardust robotic space probe. Intermediate olivines, like peridot, are a main constituent of basic igneous rocks. Concentrations of peridot in basalts and ultrabasic rocks can be mined for gem content.

The 4 C’s

Colour

Peridot comes in many shades of green, but only green. The most favored peridot colour is a richly saturated pure grass green. The highest values are given to gems with a yellowish-green hue, medium tone, and moderately strong saturation. Although pure green stones are rare, most peridots are more yellowish-green. The finest hues tend to be seen in stones weighing 10 carats and above. The gem's colour is intrinsically yellow-green, due to the presence of iron. Ferrous iron (Fe2+) creates green, while ferric iron (Fe3+) creates yellow. Higher iron levels result in a "muddier" brown colour. Traces of chromium (Cr) may make the green brighter, but do not cause the hue.

Clarity

Clarity refers to a gem's transparency and anything that can affect how it transmits light. Most peridots are usually eye clean, meaning they have no inclusions visible to the naked eye. However, most peridots do contain inclusions visible under magnification, including their distinctive "lily pads". These are reflective, disk-shaped inclusions. Eye-visible inclusions will lower a peridot's value, as will the presence of many inclusions which create a cloudy effect. Tiny black spots, actually minute mineral crystals, may also be visible under magnification. Readily visible inclusions, especially dark spots, lower the value of peridot.

Carat

Most peridot rough produces quite inexpensive stones under one carat. Rare, large sizes over three carats increase exponentially in value. Although the finest gems are generally seen in sizes above 10 carats, smaller gems cut to standard sizes are affordable and readily available. The finest large peridots come from Myanmar and Pakistan.

Cut

Peridot can take a wide variety of cutting styles, from traditional standard shapes to more experimental custom designs. It is available in a wide variety of shapes and cutting styles, including ovals, pears, rounds, emerald cuts, cushion cuts, triangle cuts, and marquise shapes. The gem is also popular for some uncommon cuts like the checkerboard. To hide inclusions, checkerboard cuts are recommended. For clear peridots, a cornered cut can work well. Peridots have high birefringence, which can cause fuzziness. To prevent this out-of-focus appearance, lapidaries must orient the stone carefully before cutting. Some peridots also have a weak pleochroic effect, showing green/yellow-green colours depending on the viewing angle. This factor can also affect gem orientation. Although peridots are typically faceted for jewelry use, cabochon cuts may reveal rare cat's eye and star stone effects.

Be Aware Of

Enhancements

Peridot is rarely treated, but might have fractures. Peridot is not enhanced or heat-treated to improve its color. Occasionally, peridot is treated with colorless oils, waxes, or resins to fill voids or surface fractures and to improve the gem’s appearance or surface luster. Any enhancements should be disclosed on the gemstone's bill of sale. Some cut peridots may be metal-foiled to improve their stability and color.

Simulants

Many peridot lookalikes or simulants are on the market. Synthetic corundum and spinel gems, as well as cubic zirconia, may be passed off as peridots. Some natural green gems can be confused with peridots, such as emeralds and demantoid garnets. However, you're more likely to find peridots presented as emeralds and demantoids than vice versa, due to their greater value. Green glass is a frequently encountered peridot simulant.

Synthetics

Scientists have synthesized both forsterite and peridot olivines using melt techniques. Chromium-doped synthetic forsterites have commercial applications for laser research and have also surfaced in jewelry. This material can be distinguished from natural forsterites and peridots due to lower specific gravity and refractive index values as well as chromium-related features. However, synthetic peridot, grown for experimental purposes, may only differ from natural gems by its inclusions. Synthetic peridots rarely appear as jewelry stones.

Final Thoughts

Buying Tips

When buying peridot, look for a pure grass-green colour free from brownish tints. The most favored peridot colour is a richly saturated pure grass green, which is usually only achieved in gems of 10 carats or larger. Smaller examples tend to show yellowish-green hues. The finest large peridots come from Myanmar and Pakistan. However, fine peridot comes from many localities. Although collectors enjoy knowing where their peridot was mined, gems that can be confirmed as coming from Zabargad Island may command a slight premium due to their historic value.

Jewellery Care

Peridot has fair to good toughness. With a hardness just below that of household dust, peridots can show scratches rapidly and chip easily. Ring stones should have protective settings, like bezels. Avoid placing peridots in tension settings, since the stress may cause them to split. Peridots also have some heat and acid sensitivity. Avoid sudden increases in heat, which could shatter them, and prolonged wear against the skin. Avoid any cleaning agents with acid as well as mechanical cleaning systems such as ultrasound, steaming, or boiling. For cleaning, use only a soft brush, mild detergent, and warm water. Peridot rings last longer if worn as a fashion wardrobe accessory rather than as a piece of everyday wear.