What is peridot? The gem from the earth's mantle and from outer space

The mantle origin: why peridot is geologically unique

All other major gem minerals form in the earth's crust, at depths typically ranging from a few kilometres (hydrothermal deposits) to perhaps 30-40 kilometres (high-pressure metamorphic environments for ruby and sapphire). Diamond is the exception, forming at even greater depths (150-200km), but is brought to the surface by kimberlite pipes. Peridot forms as the primary silicate mineral of the earth's upper mantle, at depths of 40-80 kilometres, in the olivine-dominant rock called peridotite that constitutes most of the mantle's volume (GIA Gem Reference Guide, 2006, pp. 56-57; Deer, Howie, Zussman, Rock-Forming Minerals, 1997).

Peridot reaches the surface when mantle material is brought up by basaltic volcanism (olivine phenocrysts in basalt), by tectonic processes that expose mantle rocks (obducted ophiolites), or by xenolith transport in kimberlite-type eruptions. The San Carlos Apache Reservation in Arizona, one of the world's largest peridot sources, mines olivine xenoliths from basalt flows, fragments of mantle rock carried to the surface by the volcanic activity (GIA; Wise, 2016, pp. 319-322).

Peridot in meteorites: the pallasite connection

Pallasites are a rare class of stony-iron meteorite consisting of an iron-nickel alloy matrix enclosing crystals of olivine. They are believed to originate from the core-mantle boundary of differentiated asteroids: the olivine crystals formed in the mantle region and the iron-nickel in the core, the two being mixed at the boundary region before the asteroid was disrupted by collision. When pallasites are cut and polished, the olivine crystals often appear as gem-quality peridot windows in the metallic matrix. The most celebrated examples include the Brenham meteorite (Kansas, USA), the Esquel meteorite (Argentina), and the Brahin meteorite (Belarus). Polished pallasite slices showing transparent peridot crystals are among the most extraordinary objects in mineral science and command significant prices as specimens (GIA; Wise, 2016, pp. 319-320).

Zabargad Island: the ancient source

Zabargad (also called St. John's Island or Zebirget) in the Egyptian Red Sea, approximately 50 kilometres from the coast near Marsa Alam, has been the source of peridot for at least 3,500 years and possibly as long as 3,500 BCE. The ancient Egyptians called peridot "the gem of the sun." It was mined for Egyptian royalty and later for Roman and Byzantine use. The Crusaders brought peridot to medieval Europe, where many of the large green stones set in medieval reliquaries and treasuries, assumed to be emeralds, were later identified as peridot. The Shrine of the Three Kings in Cologne Cathedral, one of the most elaborate medieval reliquaries in existence, contains 200 carats of peridot that were long believed to be emeralds (GIA; Wise, 2016, pp. 320-322).

The Zabargad deposit was rediscovered in modern times in the early 20th century and produced significant quantities of peridot until it was largely depleted by mid-century. Zabargad peridot is characterised by its high clarity and good colour; the deposit produced some of the finest large peridots in historical collections (GIA; Wise, 2016).

Pakistan and Myanmar: fine modern sources

The finest modern peridot comes from the Suppat (Sapat) valley in the Kohistan District of the Khyber Pakhtunkhwa region of Pakistan, at elevations above 4,000 metres in the Himalayan foothills. Pakistani peridot from this deposit is prized for its vivid, well-saturated green colour with minimal yellow component, the closest commercial peridot comes to a pure green rather than yellow-green. Stones above 5 carats of fine Pakistani colour and eye-clean clarity command per-carat prices of USD 100-500, modest by fine gem standards but meaningful within peridot's own quality range (GIA; Wise, 2016, pp. 322-325).

Myanmar (Burma) produces peridot from the Pyaung Gaung area in the Sagaing Division, including large and fine crystals. China (Hebei Province) is now the world's largest peridot producer by volume, supplying the commercial market. Arizona (San Carlos) remains a significant source of commercial-grade peridot, particularly in small sizes.

Colour quality in peridot

Peridot's colour is produced entirely by iron (Fe2+) in the olivine crystal structure. The colour range is relatively narrow compared to other gem species: yellow-green through vivid green to slightly brownish green. The finest peridot colour is a vivid, saturated pure green or lime green without excessive yellow or brown. Medium-dark tone at vivid saturation is optimal; pale, washed-out peridot (insufficient iron) and brownish-green peridot (iron in different coordination) are commercial-quality indicators (GIA; Wise, 2016, pp. 325-328).

Peridot commonly shows "lily pad" inclusions: partially healed fractures with a curved outline resembling lily pads on water. These are characteristic inclusions for peridot and are acceptable in commercial material. Eye-clean peridot is available at fine quality but not at all sizes; large eye-clean peridot commands meaningful premiums (GIA; Wise, 2016).

No treatment is applied to peridot commercially. The colour seen is the colour produced by iron in the olivine structure, and no standard treatment improves it. Peridot shares with garnet and spinel the no-treatment baseline that simplifies buyer assessment (GIA; AGTA).

Jyotish and peridot

Peridot is not one of the nine Navratna stones. Some contemporary Jyotish practitioners recommend peridot as an alternative for Mercury (Budh) based on its green colour, treating it as a substitute when emerald (Panna) is not accessible. This is a modern extension, not a classical prescription. Classical texts specify natural beryl coloured by chromium for Mercury. If a practitioner recommends peridot for Jyotish use, the same quality requirements apply: natural stone (peridot is untreated in any case), good colour, and adequate clarity (Behari, 1991; GIA).