The mineral olivine (when of gem-quality, it is also called peridot and chrysolite), is a magnesium iron silicate with the formula (Mg,Fe)2SiO4. It is a common mineral in the Earth's subsurface but weathers quickly on the surface. The ratio of magnesium and iron varies between the two endmembers of the solid solution series: forsterite (Mg-endmember) and fayalite (Fe-endmember). Compositions of olivine are commonly expressed as molar percentages of forsterite (Fo) and fayalite (Fa) (e.g., Fo70Fa30). Forsterite has an unusually high melting temperature at atmospheric pressure, almost 1900 C, but the melting temperature of fayalite is much lower (about 1200 C). The melting temperature varies smoothly between the two endmembers, as do other properties. Olivine incorporates only minor...'
Contributions by Vsmith, LadyofShalott, and VMS Mosaic.