felsische

Felsische is the German adjective referring to rocks and magmas that are rich in silica and light-colored minerals such as quartz, muscovite and orthoclase feldspar. In English the term corresponds to “felsic,” a classification used in igneous petrology to distinguish compositionally light, silica‑rich rocks from more mafic, silica‑poor varieties. The felsische group includes granites, rhyolites, and related volcanic and plutonic rocks that typically have densities between 2.5 and 2.7 g cm‑3. Their mineral assemblage often reflects a high proportion of felsic minerals (feldspar and quartz) and a lower proportion of ferromagnesian minerals such as pyroxene or olivine.

Felsische magmas originate from the partial melting of continental crust or from the differentiation of basaltic magmas through processes like crystal fractionation and crustal assimilation. Because of their high viscosity, felsische magmas tend to erupt explosively, producing ash‑rich pyroclastic flows and widespread tephra deposits. In the rock record, felsische lithologies are commonly associated with continental margin settings, volcanic arcs, and large igneous provinces that have undergone extensive crustal reworking.

The term also appears in economic geology, as felsische rocks frequently host valuable ore deposits, especially tin, tungsten, lithium and rare‑earth elements. Their relatively low metal content compared with mafic counterparts is offset by the enrichment of incompatible elements during magmatic differentiation. In the broader scientific literature, “felsische” is used to describe rock suites, magma series, and related geochemical signatures characteristic of high‑silica, light‑colored igneous materials.