Peridot is one of the few gemstones that occur in only one color, an olive-green. The intensity and tint of the green, however, depends on how much iron is contained in the crystal structure, so the color of individual peridot gems can vary from yellow—to olive—to brownish-green. The most valued color is a dark olive-green.Olivine, of which peridot is a type, is a common mineral in mafic and ultramafic rocks, and it is often found in lavas and inperidotite xenoliths of the mantle, which lavas carry to the surface; but gem quality peridot only occurs in a fraction of these settings. Peridots can be also found in meteorites.Olivine in general is a very abundant mineral, but gem quality peridot is rather rare. This is due to the mineral’s chemical instability on the Earth’s surface. Olivine is usually found as small grains, and tends to exist in a heavily weathered state, unsuitable for decorative use. Large crystals of forsterite, the variety most often used to cut peridot gems, are rare; as a result olivine is considered to be precious.