mafische

Mafische, in geology often written as mafic, describes igneous rocks and minerals that are rich in magnesium and iron (Mg and Fe) and relatively low in silica. The term mafic derives from magnesium and ferric iron. Mafic rocks are typically darker in color and denser than felsic rocks due to their mineral composition.

Minerals and rock types: The dominant ferromagnesian minerals are olivine, pyroxene, and amphibole, commonly accompanied by calcium-rich plagioclase feldspar. Typical mafic rock types include basalt and gabbro, which are fine- and coarse-grained varieties, respectively. Ultramafic analogs such as peridotite are richer in olivine and pyroxene and represent the upper mantle composition.

Geochemistry and textures: Mafic magmas crystallize at higher temperatures and have lower silica contents than felsic magmas, resulting in rocks with darker color and lower viscosity. They can crystallize as intrusive rocks like gabbro or erupt as volcanic rocks like basalt. Their minerals and textures reflect relatively rapid cooling in volcanic settings or slower cooling underground.

Geologic settings and significance: Mafic magmas commonly form at divergent plate boundaries and in oceanic hotspots, contributing substantially to the oceanic crust. Through processes like partial melting and fractional crystallization, mafic magmas can differentiate to produce intermediate and felsic compositions over geological time. Mafische rocks are key for understanding mantle sources, crust formation, and tectonic processes.