Peridot

Hardness: 6.5-7 on Mohs scale. Color: Olive green, yellowish-green to brownish-green. Luster: Vitreous (glassy) to oily. Crystal Structure: Orthorhombic. Cleavage: Indistinct. Specific Gravity: 3.2-4.3.

Peridot is the gem-quality variety of the mineral olivine. It forms in mafic and ultramafic igneous rocks, such as basalt, peridotite, and dunite, and also occurs in some meteorites. It crystallizes at high temperatures from magma. Geological age: Varies significantly depending on the deposit, from ancient Precambrian rocks to relatively young volcanic formations.

Primarily used as a gemstone in various forms of jewelry (rings, necklaces, earrings, bracelets). Smaller, lower-quality stones are sometimes used in abrasive applications, though this is rare given its value as a gem.

Peridot is one of the few gemstones that occurs in only one color: green. Its intensity and tint depend on the iron content within the crystal structure, with a deeper green indicating a higher iron percentage. It has been called the 'gem of the sun' by ancient Egyptians. Some peridot is extraterrestrial, found in pallasite meteorites.

In the field, peridot can be identified by its distinctive olive-green color, vitreous luster, and its presence in volcanic rocks (especially basalt flows) or as xenoliths in ultramafic rocks. It's commonly found in Arizona (San Carlos Apache Reservation) in the USA, Egypt (Zabargad Island), China, Vietnam, and Pakistan. For collectors, look for vibrant green stones with good clarity. Be aware that green glass can imitate peridot, so checking for double refraction (a distinctive optical property of peridot) or specific gravity can assist in identification.