Peridotite (per-RID-atite) is a dense, dark plutonic rock that makes up most of the upper mantle and the bottom half of the Earth's oceanic plates. It is the starting point of the geochemical process that has created the basalt and granite of the Earth's crust.
Peridotite occurs only sparsely on land, where plate collisions have brought bits of it onto the continents. Most of the photos in this gallery are from the eastern Klamath Mountains of northern California, where a major occurrence of peridotite occupies the headwaters of the Trinity River. But peridotite is also known in the Appalachian chain as well as in ophiolites around the world such as in Greece, Cyprus, Oman and Japan. See more details about peridotite.
Pervasively fractured and easily weathered, peridotite is nearly worthless as a commercial stone, although there has been talk of using its high magnesium content to absorb carbon dioxide from fossil fuel burning.
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