Peridot (also olivin or Chrysolite)
When peridot is good, it is very good, but when it is bad ... There is so much pale and lacklustre material around it is easy to forget that, with good colour and cutting, peridot can be a truly impressive and important gemstone.
Peridot only ever comes in green - pale yellowish green, olive green, bottle green or intense, vibrant apple green (the latter being the most desirable). The best cutting material comes from Pakistan, close to the Afghan border. The large fine Kashmir peridots possess a beautiful intense colour and sell for high prices.
Peridot is an idiochromatic gemstone, which means that the colour comes from the basic chemical composition of the stone itself (iron) and not from the impurities that normally colour gemstones. The material is transparent but can contain a wide selection of inclusions; the most common are "lily pads" and "fingerprints" made up of tiny drops of silica glass. You will also find dark brownish yellow leaflets of biotite mica, small crystals of pyrope garnet and spinal, small black inclusions and "silk" (a reflection of fibrous inclusions creating a silk-like appearance). Peridot does not possess great brilliance, and the lustre ranges from vitreous to greasy. Very occasionally, cat's-eye and star effects occur.
Working with peridot
• Peridot has indistinct cleavage and a conchoidal, brittle fracture. The tensions that exist within a crystal can be considerable due to the many inclusions. The characteristic "lily pads" are difficult to see and can act like cleavage planes, making faceting problematic. If the lily pad is close to the surface, the peridot may break while it is being cut and polished. If it lies well within the stone it shouldn't be a problem, and if kept parallel to the table won't be too visible.
• Check the cutting of any stone as peridot has high birefringence (the light bends at slightly different angles as it enters the crystal) and it may be possible to see a doubling of the back facets. If the material isn't oriented properly, the reflections and facet junctions will appear fuzzy as you look through the table, and the stone will lose brilliance.
• Peridot is traditionally faceted as a step cut or mixed cut in order to obtain the best colour and to reduce the risk of breakage. It can be difficult to polish and will pick up scratches relatively easy, so it is important to keep a stone set in jewelry clean and looking its best.
• Peridot is quite sensitive to heat and is easily attacked by sulphuric and hydrochloric acids, so avoid steam cleaners and chemicals. It is best not to solder or polish jewelry with the stone in situ.
Treatments and imitations
• Peridot can resemble green tourmaline, green zircon, green apatite and possibly green sapphire.
• Peridot may be oiled or opticoned to reduce the visibility of flaws. Opticon is a polymer filler that is frequently used to enhance emeralds.
Pricing peridot
The high cost of bigger, intensely coloured stones reflects not only the difficulty of finding large, "clean" rough material, but also the length of time it takes to cut and polish peridot. Peridot is readily available in paler colours, which are moderately priced.
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