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

Peridot is gem-quality olivine — a silicate mineral series ranging from forsterite (magnesium-rich) to fayalite (iron-rich), with peridot's green color coming from iron within that composition.

Why It Forms So Deep

Unlike most gemstones, which crystallize within the Earth's crust, peridot forms much deeper, in the upper mantle — a layer of the Earth most rock never reaches the surface from directly. It reaches us when volcanic eruptions carry fragments of mantle rock (called xenoliths, meaning "foreign rock") upward, embedded within basaltic lava, essentially hitching a ride to the surface during an eruption rather than forming near the surface the way most gems do.

Meteoric Peridot

Genuinely extraterrestrial peridot exists: it's been found within pallasite meteorites, a rare meteorite type containing olivine crystals embedded in a metallic iron-nickel matrix, believed to have formed at the boundary between a planetary core and mantle in a body that broke apart long ago. This material is scientifically significant but not part of commercial gem supply.

Color Consistency

Peridot's color is always some shade of green, and because that color comes from iron that's fundamentally part of the mineral's composition (not a trace impurity), it isn't typically heat-treated or color-enhanced the way many other gems are — there's little to alter, since the color is intrinsic to what the mineral is.

Historical Sources

Zabargad Island in the Red Sea (called Topazios by the ancient Greeks) was mined for peridot as early as 1500 BCE and supplied material to ancient Egypt for millennia, though the deposit is largely depleted today. Hawaii's olivine-rich volcanic sand gives certain beaches, including the well-known green sand beach near South Point, a genuinely green tint from eroded olivine grains — though this material isn't gem-grade.

Where It's Mined Today

Arizona's San Carlos deposit in the United States is a major current source, along with Pakistan and Myanmar.

Quick Facts

Mineral family: olivine (forsterite-fayalite series) — Hardness: 6.5–7 on the Mohs scale — Forms in the mantle, not the crust — Also found in pallasite meteorites — Birthstone for August — Major sources: Arizona (USA), Pakistan, Myanmar.