Monzonite

An intrusive igneous rock formed by the slow cooling of magma underground, with moderate silica content and a composition enriched in alkali metal oxides, made up mostly of plagioclase and alkali feldspar with less than 5 percent quartz. Alkali feldspar makes up between 35 and 65 percent of its total feldspar content, with the plagioclase typically ranging from sodium rich oligoclase to andesine and the alkali feldspar usually orthoclase, alongside minor amounts of hornblende and biotite. Monzonite sits within a family of closely related rocks: quartz monzonite contains more than 5 percent quartz, feldspathoid bearing varieties can carry up to 10 percent feldspathoids, syenite is richer in alkali feldspar, monzodiorite is richer in plagioclase, and latite is its volcanic equivalent, with the older term syenodiorite sometimes applied to monzonite or monzodiorite. It can form through a range of processes, including melting related to continental collision, as in Iran's Alborz Mountains, extensional crustal settings, or the partial melting of lower crust with an alkali basalt composition.