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Earth and Space Sciences · Glossary

What is Peridotite and its kinds?

Also known as: peridotite · dunite · lherzolite · harzburgite

Definition 7.1 University Earth and Space Sciences — Year 2 · Chapter 7 — Melting the Mantle

A peridotite is a coarse-grained ultramafic rock containing more than 40 %40\,\% olivine, the rest being pyroxenes and a little of an aluminous mineral (spinel or garnet). A dunite contains more than 90 %90\,\% olivine. Below that, a lherzolite contains both orthopyroxene and clinopyroxene; a harzburgite contains orthopyroxene but almost no clinopyroxene; a wehrlite contains clinopyroxene but almost no orthopyroxene. Rocks with less than 40 %40\,\% olivine are pyroxenites.

Classification of the peridotites and pyroxenites by their proportions of olivine, orthopyroxene and clinopyroxene (after the British Geological Survey’s scheme). The narrow strips along the two upper sides hold the rocks with almost no clinopyroxene (harzburgite) or no orthopyroxene (wehrlite). The red dot is the model upper mantle beneath the ridges (57, 28 and 13\,\%, renormalised without its 2\,\% of spinel).
Classification of the peridotites and pyroxenites by their proportions of olivine, orthopyroxene and clinopyroxene (after the British Geological Survey’s scheme). The narrow strips along the two upper sides hold the rocks with almost no clinopyroxene (harzburgite) or no orthopyroxene (wehrlite). The red dot is the model upper mantle beneath the ridges (57, 28 and 13 %13\,\%, renormalised without its 2 %2\,\% of spinel).
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