Peridot, sometimes called chrysolite, is gem-quality olivine and a silicate mineral with the formula of (Mg, Fe)₂SiO₄. As peridot is a magnesium-rich variety of olivine, the formula approaches Mg₂SiO₄. Its green color is dependent on the iron contents within the structure of the gem. Peridot occurs in silica-deficient rocks such as volcanic basalt and pallasitic meteorites. Peridot is one of only two gems observed to be formed not in the Earth’s crust, but in molten rock of the upper mantle. Gem-quality peridot is rare to find on Earth's surface due to its susceptibility to weathering during transportation from deep within the mantle to the surface.
In the Middle Ages, the gemstone was considered a stone that could provide healing powers, curing depression and opening the heart. Peridot is the birthstone for the month of August.