felsic

Felsic is a descriptive term in igneous petrology for rocks that are rich in silica and light-colored minerals. They typically contain high proportions of quartz and alkali feldspar, with relatively low amounts of magnesium and iron. The high silica content gives felsic rocks a lighter color and, on average, a lower density than mafic rocks.

Common felsic minerals include quartz, orthoclase (potassium feldspar), and sodium-rich plagioclase, often with mica such as muscovite or biotite as accessory minerals. Accessory minerals can also include zircon, apatite, and rutile.

Representative felsic rocks include granite and granodiorite, which are usually coarse-grained plutonic rocks, and rhyolite, quartz monzonite, or obsidian when formed as volcanic equivalents. Pegmatite is a notable coarse-grained felsic variety that hosts unusually large crystals and is economically important for certain minerals.

Felsic magmas are typically more viscous than mafic magmas, which slows crystal settling and can lead to the trapping of volatiles and explosive eruptive styles. They crystallize at relatively lower temperatures and commonly form by partial melting of existing continental crust or by differentiation of basaltic magmas.

Geologically, felsic rocks are characteristic of continental crust and are common at convergent plate boundaries and in continental batholiths. Economically and culturally significant rocks include granites used as building stone, and pegmatites that host rare elements such as lithium, tantalum, and other critical minerals.