Olivine

Olivine is a magnesium-iron silicate and one of the most abundant minerals in the Earth's mantle. Its olive-green colour gives the group its name, and it is a major component of basalt and of the mantle rock peridotite. Its transparent gem variety is known as peridot.

Identifying olivine

Olivine is fairly hard (6.5–7), glassy, and green to yellow-green, forming granular masses and stubby crystals. It occurs in dark, silica-poor (mafic and ultramafic) igneous rocks, and even in some stony-iron meteorites. On weathering it alters to brown and to serpentine.

Where it is found

Gem and specimen olivine comes from the basalt fields of Arizona, the island of Zabargad in the Red Sea, Pakistan's Sapat valley, Myanmar and China. Green olivine sand beaches form where basalt erodes, as in Hawaii.

For collectors

Sharp, gemmy green crystals and clean peridot are the most valued; olivine in meteorites and mantle xenoliths is of special scientific interest.