Olivine << AHL uh veen >> is a rock-forming mineral that consists of silicon, oxygen, magnesium, and iron. Olivine occurs primarily in dark igneous rocks rich in iron and magnesium but poor in silicon. It usually appears as grainy masses or embedded crystals. It is generally one of the first minerals to crystallize from dark-colored magma (melted rock material).
Most types of olivine range in color from clear green to yellow-green, but iron-rich varieties may be brown. Olivine is relatively hard and cannot be scratched by a knife. The most common olivine is forsterite, which is rich in magnesium. Clear green olivine used as a gemstone is called peridot.
