ultramafisiin

Ultramafisiin, or ultramafic rocks, are a class of igneous rocks defined by high magnesium and iron content relative to silica. They are typically dark-colored and dominated by minerals such as olivine and pyroxene, with comparatively little feldspar.

Common ultramafic rock types include peridotites (dunite, harzburgite, and lherzolite), pyroxenites, and serpentinites (altered ultramafics). Their composition reflects mantle derivation, either as residues after partial melting or as cumulates formed during mantle melting and melt extraction.

Formation and occurrence: Ultramafiin rocks are widespread in the Earth's mantle and in the oceanic lithosphere. They appear as mantle xenoliths carried to the surface by magmas; serpentinization, a hydrous alteration process, converts them to serpentinite and enriches minerals such as serpentine, chrysotile, and antigorite.

Geochemical and economic aspects: They typically have silica contents lower than felsic rocks and are enriched in MgO and FeO. Economic significance includes potential nickel sulfide deposits associated with dunite and harzburgite, and, in some cases, platinum-group elements. Serpentinites can form ultramafiin-derived soils that are low in calcium and rich in magnesium, influencing local plant communities. Historically, serpentinite has been a source of asbestos minerals, though modern use is highly regulated.

In geology, ultramafiin rocks are closely related to peridotite, dunite, harzburgite, lherzolite, serpentinite, ophiolite, and mantle xenoliths.