Peridotite is the dense, green engine of the Earth’s mantle and a diamond host.

Nature · Published 3 October 2026 Swipe more like this →

In short: Deep beneath our feet, peridotite dominates the upper mantle, acting as a primary source for the planet's most precious treasures. This coarse-grained, ultramafic rock is not just a geological curiosity; it is a vital window into the early formation of Earth and the complex processes occurring far below the surface.

Peridotite is defined as a coarse-grained, ultramafic igneous rock containing at least 10 percent olivine, often accompanied by pyroxenes. Because it contains less than 45 percent silica, it is classified as ultramafic, characterized by high concentrations of magnesium and iron. While often appearing as a dark, heavy stone, its name is derived from peridot, the gemstone version of its essential mineral, olivine. In its natural state, peridotite can exhibit a spectrum of colors, though it is most commonly recognized by its olive-green hue.

The rock occurs in four primary geologic environments: as part of tabular-layered igneous complexes, within alpine-type mountain belts, inside volcanic pipes as kimberlite, and as dikes or irregular masses. These formations provide scientists with critical samples from depths ranging from 30 km to 200 km or more. By studying these nodules, researchers can analyze isotope ratios that record conditions from when the Earth was first formed, offering a unique perspective on the planet’s early mantle composition.

Beyond its scientific value, peridotite is economically significant as the ultimate source of all chromium ore, naturally occurring diamonds, and nearly all chrysotile asbestos. It also serves as a major host for talc and platinum metals. Because peridotite is easily altered to serpentine, it is frequently found in a weathered state, yet these weathered deposits remain massive potential sources of iron, nickel, cobalt, and chromium, particularly in warm, humid climates where they have transformed into soil-related deposits.

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