Peridot is the gem variety of the mineral olivine. Its chemical composition includes iron and magnesium, and iron is the cause of its attractive yellowish green colors. The gem often occurs in volcanic rocks called basalts, which are rich in these two elements.
Geologists believe both types of deposits relate to the spreading of the sea floor that occurs when the earth’s crust splits, and rocks from its mantle are pushed up to the surface. Sometimes—as in Myanmar— these rocks can be altered, deformed, and incorporated into mountain ranges by later earth movements.
Rarely, peridot can have an extraterrestrial source, being contained in meteorites that have fallen to earth.