Peridot is the gem variety of the mineral olivine. Its chemical composition includes iron and magnesium, and iron is the cause of its attractive yellowish-green colors. The gem often occurs in volcanic rocks called basalts, which are rich in these two elements.
Peridot has always been associated with light. In fact, the Egyptians called it the “gem of the sun.” Some believed that it protected its owner from “terrors of the night,” especially when it was set in gold. Others strung the gems on donkey hair and tied them around their left arms to ward off evil spirits.
The word peridot comes from the Arabic “faridat,” which means “gem.” Most peridot formed deep inside the earth and was delivered to the surface by volcanoes. Some also came to earth in meteorites, but this peridot is extremely rare.
Early records indicate that the ancient Egyptians mined a beautiful green gem on an island in the Red Sea called Topazios, now known as St. John’s Island. From the earliest times, people confused this stone—now known to be peridot—with other gems. It was one of many labeled as “topaz.”
Some historians believe that Cleopatra’s famous emerald collection might actually have been peridot. People in medieval times continued to confuse peridot with emerald. For centuries, people believed the fabulous 200-ct. gems adorning the shrine of the Three Holy Kings in Germany’s Cologne Cathedral were emeralds. They are, in fact, peridots.
Peridot is readily available for many types of jewelry. It can be very affordable and attractive, and can come in large sizes and very intense colors to satisfy the most discriminating colored gemstone connoisseur.
Peridot’s color ranges from pure green to yellowish-green to greenish-yellow. The finest hue is green without any hint of yellow or brown. Although the best peridot is a pure grass-green, most peridot is yellowish-green. Lower-quality peridot is brownish.
Pure green stones are rare, and most peridots are more yellowish-green. The higher-quality stones have an intense color. Most of the stones with the finest color come from Myanmar and Pakistan.
Most fine peridot is eye-clean. Tiny black spots, actually minute mineral crystals, may be visible under magnification. Other inclusions common in peridot are reflective, disk-shaped inclusions called “lily pads.” Readily visible inclusions, especially the dark spots, lower the value of peridot. There’s a dramatic drop in value for light-colored material with prominent dark inclusions.
Peridot is cut in a wide variety of shapes and cutting styles. Production includes all the standard gem shapes such as ovals, pears, rounds, emerald cuts, cushion cuts, triangle cuts, and marquise shapes.
Standard peridot cuts for the jewelry industry include a wide range of shapes and sizes. The gem is inexpensive in smaller sizes, but prices rise for gems above 10×8 mm. The finest large peridots come from Myanmar— formerly Burma—and, more recently, from a source high in the Himalayas of Pakistan. More-standard sizes and qualities come mostly from the United States (Arizona) and China.
- MINERAL:Olivine – Gem variety of the mineral olivine: found in peridotite rock from the
earth’s upper mantle.
- CHEMISTRY: (MgFe)2SiO4
- COLOR: Yellowish green – The color range for peridot is narrow, from a brown-green color to yellowish-green to pure green. Yellowish green is the most common peridot color seen in jewelry.
- REFRACTIVE INDEX: 1.65 to 1.69
- BIREFRINGENCE: 0.035 to 0.038
- SPECIFIC GRAVITY: 3.34
- MOHS HARDNESS: 6.5 to 7
(GIA Gem Encyclopedia Peridot, 2015)