Olivin

Olivin, commonly referred to as olivine in English, is a magnesium iron silicate mineral in the nesosilicate group with the formula (Mg,Fe)2SiO4. It forms a continuous solid-solution series between the magnesium-rich endmember forsterite (Mg2SiO4) and the iron-rich endmember fayalite (Fe2SiO4).

Olivin crystallizes in the orthorhombic system and typically occurs as euhedral to granular crystals in high-temperature rocks. Its color ranges from olive-green to yellow-green, and it often appears in masses or elongated crystals. The mineral has a vitreous luster, a hardness of about 6.5–7 on the Mohs scale, and shows no distinct cleavage, tending to fracture conchoidally. Densities increase with iron content, with forsterite being lighter than fayalite. Optical properties include high refractive indices and moderate birefringence, which vary across the solid-solution series.

Geologically, olivine is a major constituent of mafic and ultramafic rocks such as dunite, peridotite, and basalt, and it is a prominent component of the Earth’s upper mantle. It forms at high temperatures and contributes to mantle geotherm and magma evolution studies. Olivine is also found in some meteorites, including pallasites.

Economically, gem-grade olivine is known as peridot and is used as a gemstone, though most olivine is consumed as a refractory and in industrial applications due to its high melting point and chemical stability. The name olivine derives from Latin olivinus, meaning olive-green, reflecting its characteristic color.