Granitoids

Granitoids are a broad assemblage of coarse-grained, silica-rich igneous rocks that crystallized from magma within the crust. The term encompasses granite and related rock types such as granodiorite, tonalite, quartz monzonite, and adamellite, which share a dominantly quartz- and feldspar-rich mineralogy with relatively little ferromagnesian material.

They typically form through crystallization of silica-rich magmas generated by partial melting of existing crustal rocks or by differentiation of mantle-derived magmas. Crystallization occurs at depths and under cooling conditions that produce coarse grains, yielding a phaneritic texture. Granitoids are strongly associated with continental crust formation, often occurring in large plutons or batholiths within convergent-margin and post-orogenic tectonic settings.

Mineralogy is dominated by quartz, alkali feldspar, and plagioclase, with minor dark minerals such as biotite, hornblende, or muscovite, and various accessory minerals including zircon and apatite. Texture is typically hypidiomorphic and granular, with little to no pegmatic development in plutonic rocks; exsolution of alkali feldspar and zoning in minerals can occur.

Classification uses mineral proportions and aluminum saturation. Common granitoid types include granite, granodiorite, tonalite, and quartz monzonite; distinctions depend on the relative amounts of plagioclase and alkali feldspar and the presence or absence of quartz. The terms peraluminous vs metaluminous and I-type vs S-type reflect crustal sources and tectonic history, though these categories are not universal.

Granitoids are a major component of the continental crust, forming large intrusions called batholiths and contributing to crustal evolution, ore formation, and geological mapping. They are widely quarried for construction and dimension stone.