Olivine is the mineral that forms the gemstone peridot.
Peridot is the gem-quality variety of olivine, a mineral group composed mainly of magnesium-iron silicates. Its green color comes from iron within the crystal structure. Unlike many gemstones whose colors can result from trace impurities, peridot’s characteristic green is intrinsic to its composition.
Olivine is an important mineral in Earth’s mantle and occurs in many mafic and ultramafic igneous rocks. It crystallizes early from magnesium- and iron-rich magma. Large crystals can also occur in some volcanic rocks and in peridotite, a rock thought to represent much of the upper mantle.
Peridot has been used in jewelry for thousands of years. Ancient sources included deposits on Zabargad Island in the Red Sea, historically called St. John’s Island. Peridot should not be confused with emerald: emerald is a green variety of beryl, while peridot belongs to the olivine group.