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Peridot is a gem-quality olivine and a (Mg, Fe)2SiO4 type silicate mineral. The formulation approaches Mg2SiO4 because it is a magnesium-rich olivine (forsterite). The green colors of the gem depend on the structure of the iron contents. It occurs both in volcanic basalt and in pallastic meteorites in silica-deficient rocks. It is one of the two gems that have been observed to form in the rock of the upper mantle rather than in the earth’s crust. It’s gem-quality is unusual on the earth’s surface due to its environmental sensitivity when transporting deep into the mantle.