olivín

Olivín is a group of silicate minerals that form a solid solution series between two endmembers, forsterite and fayalite. The general formula for olivine is (Mg, Fe)2SiO4, where the ratio of magnesium to iron can vary widely. Forsterite (Mg2SiO4) is the magnesium-rich endmember, while fayalite (Fe2SiO4) is the iron-rich endmember. As the iron content increases, the color of the olivine typically changes from a pale green to a darker, yellowish-green or even black. Olivine is a very common mineral found in the Earth's upper mantle, and it is also a significant component of mafic and ultramafic igneous rocks such as basalt, gabbro, and peridotite. It is often found as phenocrysts in volcanic rocks. Gem-quality olivine is known as peridot and is typically a vibrant green. Peridot is mined in various locations worldwide, including Egypt, Myanmar, Pakistan, and the United States. Olivine is relatively resistant to weathering but can be altered to serpentine and other secondary minerals over geological timescales. Its presence and composition in rocks provide valuable information about the conditions under which those rocks formed and the tectonic setting.