What does felsic mean?
Felsic is a geological adjective describing igneous rocks, magmas, and minerals that are rich in silica and dominated by light-colored minerals, especially feldspar and quartz. Felsic rocks—granite and rhyolite are the best-known examples—are typically pale in hue, relatively low in density, and high in viscosity when molten, which is why felsic lavas tend to trap gases and drive explosive eruptions. The word was coined in the early twentieth century as a blend of 'feldspar' and 'silica', mirroring its counterpart 'mafic', which covers dark, iron- and magnesium-rich rocks such as basalt and gabbro. Though firmly technical, felsic is essential vocabulary for understanding how volcanologists and petrologists classify the rocks that make up continental crust, and it offers a compact way to link a rock's chemistry, color, and eruptive behavior in a single term.
(Of igneous rock, magma, or lava) rich in silica and containing abundant light-colored minerals such as feldspar and quartz.
"Rhyolite is the volcanic equivalent of granite, both being distinctly felsic."
Almost always used attributively before the noun it modifies.
A felsic mineral; one of the light-colored, silica-rich minerals of which felsic rocks are chiefly composed.
"Quartz and muscovite are among the common felsics of granite."
Less common than the adjectival use; found mainly in technical geological writing.
Used only for the rare noun sense referring collectively to felsic minerals.
"The thin section reveals a groundmass crowded with felsics."
Coined by mashing together 'feldspar' and 'silica', this word quietly sorts nearly every volcanic rock on Earth into one of two camps.
Reviewed by Deb Chak, Editor. AI-assisted content curated by RJS Tech Solutions LLP.
Etymology of felsic
The word felsic was coined in English in the early twentieth century from the initial syllables of 'feldspar' and 'silica', reflecting the minerals that characterize the rocks it names. It arose alongside the parallel term 'mafic', built similarly from 'magnesium' and 'ferrum' (iron). Both terms belong to the specialized vocabulary of petrology, where they remain the standard basis for classifying igneous rocks by chemical composition.
Related word forms
How felsic is actually used
A technical term used almost exclusively in geology and earth science; it carries no figurative or everyday usage. It is most often encountered as an attributive adjective ('felsic rock', 'felsic magma') and contrasts systematically with 'mafic'.
Easily confused with felsic
Mafic describes the opposite class of rocks—dark-colored and rich in magnesium and iron—whereas felsic rocks are light-colored and silica-rich.
Feldspar is a specific group of minerals, while felsic is a broader term describing rocks or magmas rich in feldspar and silica.