Peridotite bodies exposed at Earth’s surface are rapidly attacked by weathering. They can then be obscured by soil, sediment, glacial till, and vegetation. Finding a peridotite body as small as a kimberlite pipe, which might be only a few hundred yards across, can be very difficult. Because peridotite often has magnetic properties that are distinctly…

Some peridotites contain significant amounts of chromite. Some of these form when a subsurface magma slowly crystallizes. During the early stages of crystallization, the highest-temperature minerals such as olivine, orthopyroxene, clinopyroxene, and chromite begin to crystallize from the melt. The crystals are heavier than the melt and sink to the bottom of the melt. These…

The formation of diamonds requires very high temperatures and pressures that only occur on Earth at depths of 100 miles below the surface and at locations in the mantle where temperatures are at least 2000 degrees Fahrenheit. The diamonds are delivered to the surface in pieces of rock, known as xenoliths, which are torn from…

Earth’s mantle is thought to be composed mainly of peridotite. Some of the occurrences of peridotite on Earth’s surface are thought to be rocks from the mantle that have been brought up from depth by deep-source magmas. Ophiolites and pipes are two structures that have brought mantle peridotite to the surface. Peridotite is also found…

Peridotite is a rock type that is more representative of Earth’s mantle than of the crust. The minerals that compose it are generally high-temperature minerals that are unstable at Earth’s surface. They are quickly altered by hydrothermal solutions and weathering. Those that contain magnesium-oxide-bearing minerals can alter to form carbonates, such as magnesite or calcite, which are much…

The peridotite “family” contains a number of different intrusive igneous rocks. These include lherzolite, harzburgite, dunite, wehrlite, and kimberlite (see photos). Most of them have an obvious green color, attributed to their olivine content.

Peridotite is a generic name used for coarse-grained, dark-colored, ultramafic igneous rocks. Peridotites usually contain olivine as their primary mineral, frequently with other mafic minerals such as pyroxenes and amphiboles. Their silica content is low compared to other igneous rocks, and they contain very little quartz and feldspar. Peridotites are economically important rocks because they often contain chromite – the only ore of chromium; they can be source rocks for diamonds;…