On the nature of peridot
Peridot is the gem-quality variety of the mineral forsterite. Not only is peridot, also known as olivine, found in the earth’s upper mantle but it is also the most abundant material in the earth's crust. Peridot and diamonds are the only gemstones to form below the crust. Usually, it is brought to the surface by volcanic eruptions.
Peridot's color, yellow-green, is a result of the rather high percentage of iron found in this gemstone. Too much iron, however, can result in an unattractive shade of green with brown undertones.
On finding peridot and what to look for
The most important source of peridot for the ancient Egyptians, Greeks, and Romans was an island off the coast of Egypt in the Red Sea. Throughout history, this island has been known by many names. The Greeks and Romans called it Topazios. Peridot was originally called topazion after the island and it wasn't until the 18th century that the gemstone was renamed peridot. The island is known today as Zabargad, the Arabic name for peridot. Other important sources of peridot include Burma, China, Zambia, and Pakistan but 90% of known peridots come from the San Carlos Apache reservation in Arizona and New Mexico.
Peridots are evaluated according their color, clarity, cut, and carat weight.
Color. A rich color of grass-green without brownish tints is considered best. However, this particular shade is usually only present in stones ten carats or more. Smaller peridots tend to have yellowish-green or brown hues which lower their value.
Clarity. The best-quality peridot will not have inclusions that are visible to the eye, although they may have a few tiny black spots that can be seen under a microscope. These black spots are actually minute mineral crystals. Peridots may also have "lily pads," which are reflective, disk-shaped inclusions.
Cut. A skilled lapidary will enhance a peridot's body color by choosing among the many cuts often used on this gemstone: ovals, pears, rounds, emerald cuts, cushion cuts, triangle cuts, and marquise shapes.
Carat. The finest peridots tend to be over ten carats. Unlike many other gemstones, there are fine specimens reaching over 50 carats in circulation. That said, smaller peridots cut to standard sizes and shapes are affordable and easy to come by.
Historical notes and other interesting facts about peridot
Egyptian beads. More than 3,000 years ago Egyptians fashioned beads from peridot.
Island of the Dead. For many centuries, the only place to find peridot was on an island in Egypt. The island, now known as Zabargad (Arabic for peridot), once was called by other names including Island of the Serpents, Island of the Dead, and Topazios.
Sealed with peridot. In early Mediterranean and Middle Eastern times, peridot was one of the favored stones used as seals in signet rings. Along with jasper, sardonyx, and sard, it was soft enough to carve but still hard enough to retain its lines after use.
Delivered by the crusaders. During the Crusades, peridot was brought back to Europe and used to adorn religious objects.
A throne studded in peridots. Reclining in the treasure house at Turkey's Topkapi Palace is a throne made in the late 1500s adorned with 957 peridots.
The evening emerald. Traditionally gemstones have been thought to contain specific powers. Peridots were considered useful in warding off evil spirits and protecting against the terrors of the night. Agatharchides, a Greek historian and geographer popular in the 2nd century BC, described the stone as "invisible during the day since it is overwhelmed by the brightness of the sun; but when night falls, it shines in the dark and is visible from afar wherever it may be."
Possibly worn by aliens from outer space? Peridot can be found in pallasite, one of the most beautiful types of meteor which is comprised of an iron-nickel matrix interlaced with olivine crystals of peridot quality. In 2003 scientists discovered, by way of a NASA spacecraft, that a large area of Mars is covered in peridot crystals. And in 2005 peridot was found in comet dust brought back from a space probe.
Seeing double. Peridot has extremely high double refraction: when you look closely through the gem, you can see two of each pavilion facet.
Resources and further reading
The Gemological Institute of America's Gem Encyclopedia.
Gemstones of the World. By Walter Schuman. Our go to book at Grimballs.
Jewels: A Secret History. By Victoria Finlay. An non-fiction adventure through time and place exploring the history of gems.
Smithsonian Institution National Museum of Natural History's Gem Gallery.