ultramafias

An ultramafia is a rare type of igneous rock that is primarily composed of the mineral olivine, often exceeding 90% of its volume. The term "mafic" refers to rocks rich in magnesium and iron, and "ultra" signifies an even higher proportion of these elements. Peridotite is the most common ultramafic rock, and its varieties include dunite and lherzolite.

These rocks typically form deep within the Earth's mantle, where temperatures and pressures are extremely high. They are brought to the surface through tectonic processes such as mantle plumes, subduction zones, and ophiolite emplacement. Because they originate from the mantle, ultramafias are considered a primary source of magma generation when they undergo partial melting.

Ultramafic rocks are generally dense and dark-colored. While not as common at the Earth's surface as more silica-rich rocks, they are significant in understanding mantle composition and dynamics. Their mineralogy, particularly the presence of olivine and pyroxenes, makes them susceptible to alteration by water, forming serpentine minerals. This alteration process is known as serpentinization and can play a role in geological hazards and the cycling of elements. Economically, some ultramafic intrusions are associated with important mineral deposits, such as nickel, platinum-group elements, and chromite.