Peridot ( PERR-ih-dot, -⁠doh), sometimes called chrysolite, is a deep yellowish-green transparent variety of olivine. Peridot is one of the few gemstones that occurs in only one color.

Peridot can be found in mafic and ultramafic rocks occurring in lava and peridotite xenoliths of the mantle. The gem occurs in silica-deficient rocks such as volcanic basalt and pallasitic meteorites. Peridot is one of only two gems observed to be formed not in the Earth’s crust, but in the molten rock of the upper mantle. Gem-quality peridot is rare on Earth's surface due to its susceptibility to weathering during its movement from deep within the mantle to the surface. Peridot has the formula of (Mg, Fe)₂SiO₄. Peridot is one of the birthstones for the month of August.

Etymology and Appearance: The origin of the name "peridot" is uncertain, possibly derived from Anglo-Norman or Arabic words. It is a gemstone that occurs only in an olive-green color, with its intensity and tint depending on iron content. Peridot can vary from yellow to olive to brownish-green.

Mineral Properties: Peridot is made of isomorphic olivine, silicate, magnesium, and iron in an orthorhombic crystal system. It does not oxidize at natural surface temperatures but starts to oxidize slowly at 600°C.

Occurrence: Olivine is the source of peridot. Gem-quality peridot is rare due to its chemical instability on Earth's surface. Large crystals of forsterite, used to cut peridot gems, are also rare. Peridot can be found in meteorites and can be differentiated by size and composition. The San Carlos Apache Indian Reservation in Arizona is the principal source of peridot olivine today, with other sources around the world.

Gemology: Peridot is biaxial, with three principal axes, and its refractive index and specific gravity vary depending on iron concentration. Inclusions are common, with their presence depending on location and geological conditions.

Cultural History: Peridot has been prized for its alleged protective powers, though there is no scientific evidence for such claims. It is sometimes mistaken for emeralds and other green gems. Peridot is the birthstone for August, and the largest cut peridot olivine is a 310-carat specimen in the Smithsonian Museum.