What Is Peridot? A Gem That Forms Deep in the Earth's Mantle

Peridot is gem-quality olivine, and its formation story is unusual: most gemstones crystallize in the Earth's crust, but peridot forms much deeper, in the upper mantle. It reaches the surface when volcanic eruptions carry fragments of mantle rock upward, embedded in basalt.

Its color is always some shade of green, caused by iron within the crystal structure — unlike many gems, it isn't typically heat-treated or color-enhanced, since there's little to improve on. Genuinely extraterrestrial peridot even exists: it's been found inside pallasite meteorites. Commercial sources on Earth include Arizona's San Carlos deposit, along with Pakistan and Myanmar. It's the traditional birthstone for August.