Peridot: the gem of light

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Peridot is a gem-quality form of the mineral olivine, a name given to a mineral series with the two end members being iron-rich fayalite and magnesium-rich forsterite.

The two minerals form a series where the iron and magnesium are substituted for each other without much effect on the crystal structure.

Virtually all specimens of the two minerals contain both iron and magnesium. Most peridot is actually the magnesium-rich forsterite and its colour is caused by the presence of iron ions.

Olivine is found in ultramafic igneous rocks and in marbles formed from metamorphosed impure limestones.

Peridot is also known as the gemstone born in fire: crystals of peridot are often found in the rocks erupted by volcanoes. They can also be found in certain types of meteors called a “Pallisite”, polished slices of which reveal a metallic nickel-iron matrix peppered with peridot crystals.

Because the iron that creates the colour is an integral part of its structure, peridot can only be found in green, yet hues include a summery yellow-green, grass green, and olive green.

Peridot crystal

The best examples of peridot have iron percentages less than 15 per cent, and include nickel and chromium as trace elements that may also contribute to the best peridot colour. Some stones have a tinge of brown and are less-highly-prized.

The name peridot is derived from the Greek word peridona, meaning to give richness. The Romans called peridot the evening emerald, since its green colour did not darken at night and was clearly visible by lamplight. Perhaps it is for this reason that peridot was often used to decorate medieval churches.

Known by the ancient Egyptians as the gem of the sun, peridot has enjoyed a mystical reputation for its alleged powers including its ability to ward-off anxiety, enhance speech and bring success to relationships.

The Greeks believed that it bestowed royal dignity upon its wearer. Peridot had the reputed power to drive away evil spirits when pierced, strung on donkey hair and worn over the left arm. But the power was considered to be even more intense when the stone was set in gold.

It was also believed to strengthen any medicine drunk from goblets carved from the gemstone, if ever a piece large enough is found.

Peridot is a comparatively soft stone, with a hardness of around 6.5 on Moh's scale. It is thus susceptible to abrasion and a loss of polish. There is also a distinctive cleavage parallel to the crystal's vertical axis. So while peridot is apt for embellishment of earrings and brooches, its use in bracelets and rings is not as popular.

The earliest-recorded production of peridot was in 70 AD from St Johns Island in the Red Sea – about 40km off the coast of Egypt.

Most of the earliest-known peridot gems came from this location and small amounts of material are still being produced there today. Large, fine-quality, peridot gems are being produced from deposits in Myanmar also.

These deposits were well known for producing 20 to 40-carat stones of superb colour and clarity. Specimens are vivid, light green with fine inclusions that bear a silky shine.

The most beautiul stones come from the border area between Pakistan and Afghanistan.