Igneous Rock: Peridotite

Peridotite is coarse grained and contains high content of magnesium, and is the dominant part of the Earth's upper mantle. It consists mostly of the minerals olivine and pyroxene. They can be either layered or massive, and both types can have varying textures of crystal structure. It is usually a dark green color, depending on the level of olivine comprising it.

Peridotite is usually found beneath the Earth's crust, and is rarely visible on the surface because it is so unstable when reacting with water. Types of peridotite located near the crust are usually transformed through varying processes to become other minerals, like serpentine. One type of serpentine is commonly known as asbestos.

The Smith River in California is one of the Earth's largest exposures of peridotite, at the depth of 10-50 km.