Peridot

Hardness: 6.5-7 on Mohs scale. Color: Typically olive green, but can range from yellowish-green to brownish-green. Luster: Vitreous (glassy) to oily. Crystal Structure: Orthorhombic, often forming short, prismatic crystals; however, in jewelry, it is usually found as faceted gemstones without apparent crystal forms. Cleavage: Poor in two directions. Specific Gravity: 3.2-4.4, depending on the iron content.

Peridot is the gem-quality variety of the mineral olivine. It forms in mafic and ultramafic igneous rocks such as basalt, peridotite, and dunite. It crystallizes from magma deep in the Earth's mantle and is brought to the surface through volcanic activity. Some peridot can also be found in pallasite meteorites, indicating an extraterrestrial origin. Geological Age: Peridot is found in rocks ranging from Proterozoic to Cenozoic eras, with some deposits being tens of millions of years old.

Primarily used as a gemstone in jewelry due to its attractive green color and moderate hardness. It is popular in rings, necklaces, earrings, and bracelets. Historically, it was used for decorative objects and amulets. In industry, the non-gem quality olivine is used in refractories, metallurgy, and as an abrasive.

Peridot is one of the few gemstones that occurs in only one color, green, with the intensity of the green depending on the iron content within the mineral's structure. It is the birthstone for August. Ancient Egyptians called it the 'gem of the sun' and believed it protected against nightmares and evil spirits. The largest faceted peridot is 310 carats and is located at the Smithsonian Museum.

Key identifying features include its distinctive green color, often with a slight yellowish tint, and its vitreous luster. When examined closely, some peridot stones might exhibit a phenomenon called 'doubling,' where the back facets appear doubled when viewed through the front facets due to its high birefringence. It is commonly found in volcanic rocks, especially basalts, in locations such as the San Carlos Apache Reservation in Arizona (USA), China, Vietnam, Pakistan, and Myanmar. For field identification, look for small, glassy green crystals within volcanic rocks. Due to its relative softness compared to other popular gemstones, care should be taken to avoid scratches. Collectors often seek well-formed crystals or large, clear faceted stones.