Felsique

Felsique is a geological term used to describe a class of igneous rocks that are high in silica and rich in light-colored minerals. The word is closely related to the term felsic, and in some languages or texts felsique serves as an equivalent spelling. Felsique rocks are contrasted with mafic rocks, which contain relatively more magnesium and iron and tend to be darker in color.

Felsique rocks are characterized by mineral assemblages dominated by quartz and alkali feldspars (such as orthoclase) and plagioclase. They may also contain light-colored mica minerals (like muscovite) and accessory minerals such as zircon or tourmaline. Chemically, they typically have high silica (SiO2) content and elevated alkali oxides (K2O, Na2O), with lower magnesium and iron content than mafic rocks. Their color index is generally low, giving them a pale appearance.

Textures in felsique rocks range from coarse-grained intrusive varieties to fine-grained extrusive varieties. Common examples include granites and granodiorites (intrusive) and rhyolites and obsidians (extrusive). The high silica content and low viscosity of felsique magmas influence their crystallization, often producing rocks with large, well-formed mineral grains in plutonic settings or rapid cooling textures in volcanic environments.

Felsique rocks form chiefly in continental crust settings where partial melting of existing rocks or subduction-related processes generate silica-rich magmas. They play a key role in understanding crustal differentiation, tectonic history, and mineral systems. Commercially, felsique rocks such as granite are valued for construction and decorative stone, while their mineralogy can host certain ore deposits in hydrothermal systems.