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| Peridot fact file | |
| Crystal Structure: Orthorhombic Chemical Composition: Chrysolite or Olivene – Magnesium/Iron Silicate ( (Mg,Fe)2SiO4 ) Hardness: 6 ½ to 7 MOHS | Refractive Index: 1.654 to 1.690 Colors: Transparent yellowish-green, bottle green |
Peridot, the green volcanic gem is the August birthstone.
Also nicknamed as “evening emerald”, Peridot is considered to have the power to ward off evil spirits. Geologically, Peridot is composed of the mineral olivine and gets its green color from its iron component.
Physical and Chemical Properties
Chemical composition
Peridot is a gem variety of the mineral Chrysolite or Olivene and its chemical formula is given by: (Mg,Fe)2SiO4. The ratio of Magnesium and Iron in the crystal is highly variable and the name Forsterite (Fo) is applied to Magnesium-rich/ Iron-poor crystals whereas the name Fayalite (Fa) is applied to Magnesium-poor/ Iron-rich crystals. Crystals are often flattened and much peridot is found in granular masses or embedded grains in a finer grained basic igneous rock such as basalt or gabbro. Peridot has a distinct cleavage (breakage along preferred planes) and a conchoidal (shell-like) fracture. It ranges from about 6.5 to 7 on Mohs hardness scale. Peridot is fairly dense with a specific gravity ranging from about 3.27 to 3.37. The refractive indexes (the numerical measures of how much a light beam is bent and slowed down when it enters a substance) of peridot range from about 1.654 to 1.690. Peridot has three refractive indexes, two of which remain fixed and one that is variable and numerically between the upper and lower index. The birefringence of peridot is fairly high: 1.690 – 1.654 = 0.036. This fact is very valuable to the jeweler or gemologist for when one views a faceted peridot through the table of the stone, the junctions of adjacent facets are strongly doubled. Inclusions in peridot are also strongly doubled. Peridot may have small inclusions of biotite (brown), chromite (black), pyrope garnet (dark red), spinel (tiny octahedra) or liquid and gas-filled inclusions that resemble fried eggs. The strong doubling of facet junctions and inclusions as well as the pale yellowish green color are very characteristic of peridot.
Colors
Peridot has a distinctive olive or bottle green color that sometimes has a brownish tinge. The green color is due to the iron presence, while the brownish tint is the result of higher iron concentration.
Healing Properties and Interesting Information
Where Found
Some fine gem peridot has recently been found in Pakistan. Volcanic bombs containing small peridot crystals of nice gem quality have been found in basaltic rocks New Mexico and Arizona. The San Carlos Apache Reservation in Arizona has yielded numerous stones that are in the 4 to 5 carat range as uncut rough. In recent times, some large finished stones from Myanmar in the 40 to 50 carat weight range were recorded. The earliest known source of peridot is the Egyptian island Zabargad (St. John’s Island), located in the Red Sea. Peridot has been mined on this island for more than 3,500 years, and good crystals still abound there. Other sources of this august birthstone include Australia, Brazil, Myanmar, Norway, and the United States (Hawaii and Arizona). Peridot has even been found in some meteorites.
History, mythology
Historically, the use of peridot goes back several thousands of years. Egyptians enslaved the people of St. John’s Island in the Red Sea and forced them to mine peridot for use in ornaments and jewelry. Fine gem peridot has also been mined near Mogok, Burma, and Minas Gerais, Brazil. Peridot is among the oldest known gemstones. As early as 1575 to 1350 b.c.e. the ancient Egyptians used peridot beads in their ceremonial jewelry. Since antiquity, peridot has been regarded as a symbol of the sun and was worn in amulets to prevent nightmares. Late in the Ottoman Empire (1300 to 1918), peridot was a highly prized gem, and Turkish Sultans amassed some of the world’s largest collections of the gemstone.
Buying and Caring tips
Tips for Buying Peridot Jewelry
Prices for these gemstone range between $5 and $100 per carat for a one-carat stone. Common substitutes for peridot include synthetic sapphire and synthetic spinel. Both of these are isotropic (have one refractive index) and doubling will not be observed. Glass will show some elongated bubbles and no doubling.
Tips to take care of Peridot Jewelry
Warm soapy water and a soft brush is your best bet. Do not use an ultrasonic cleaner or steamer. Avoid contact with acids.