The mineral olivine is a magnesium iron silicate with the formula (Mg+2, Fe+2)2SiO4. Thus it is a type of nesosilicate or orthosilicate. It is a common mineral in the Earth's subsurface but weathers quickly on the surface.
Olivine incorporates only minor amounts of elements other than oxygen, silicon, magnesium and iron. Manganese and nickel commonly are the additional elements present in highest concentrations.
Olivine gives its name to the group of minerals with a related structure (the olivine group) which includes tephroite (Mn2SiO4), monticellite (CaMgSiO4) and kirschsteinite (CaFeSiO4). Olivine gemstones are called peridot and chrysolite.
This post is part of the Friday Greens meme.