monzonites

Monzonite is a coarse‑grained intrusive igneous rock characterized by a relatively equal mix of plagioclase feldspar and alkali feldspar, with little quartz. It sits in the feldspar-dominated, granitic family of rocks and is typically distinguished from quartz-rich varieties by its low quartz content.

The essential minerals of monzonite are plagioclase and alkali feldspar (such as orthoclase or microcline), usually in near-equal proportions. Quartz is generally a minor constituent, often less than about 20%. Mafic minerals, including biotite, hornblende, or pyroxene, occur as accessories or minor phases. The texture is typically holocrystalline and phaneritic, reflecting slow cooling underground; porphyritic varieties with large feldspar phenocrysts also occur.

In the spectrum of felsic intrusive rocks, monzonite is intermediate between granite and diorite/granodiorite in terms of feldspar ratios and quartz content. Rocks with notably higher quartz content are termed quartz monzonite, while those with more plagioclase than alkali feldspar and relatively more quartz are granodiorite or granite. Monzonite may host various accessory minerals such as magnetite, apatite, and zircon.

Occurrence and formation are linked to crustal differentiation processes, often in continental or continental-margin settings. Monzonites form as plutonic bodies—stocks, batholiths, dikes, and sills—where magma crystallizes at depth before or during crustal uplift. They are widespread in many ancient and modern continental regions and are commonly associated with tectonic environments involving crustal melting and arc-related magmatism.