felsic
Enriched in minerals predominantly composed of the lighter elements such as silicon, oxygen, aluminium, sodium, and potassium.
felsic: light-colored rock rich in silica and alkali metals
Felsic rock is igneous material dominated by light-colored minerals: quartz, feldspars (particularly plagioclase feldspars rich in sodium and potassium), and muscovite mica. These minerals are built from silica (SiO2) and alkali elements, which is why the term exists: "fel" from feldspar and "sic" from silica. The result is a rock body that is typically pale gray, pink, or white, with a low density relative to mafic rocks, and a silica content above 65 percent by weight.
Granite is the archetypal felsic rock. Formed by slow cooling of magma deep underground, granite's large crystals reflect extended crystallization time. Rhyolite is its extrusive equivalent, erupted from volcanoes and cooling rapidly to form fine-grained texture. Pegmatite, an extreme variant, exhibits very coarse crystals and often concentrates rare elements like lithium, beryllium, and tantalum, making it valuable for specialty extraction. Aplite represents the opposite extreme: very fine grained felsic rock forming at magma margins where cooling is rapid.
Economic significance and extraction challenges
Felsic rocks are quarried for aggregate, decorative stone, and silica sand. Granite quarrying involves drilling, blasting, and block extraction; dimensional stone commands higher prices than crushed material. Feldspar itself is extracted from pegmatites and granites for ceramics, glass manufacture, and enamel production. The minerals present determine value: potassium feldspar is prized over plagioclase for some applications.
Processing felsic rock presents fewer metallurgical obstacles than mafic material because iron and magnesium content is minimal. However, quartz hardness complicates crushing and grinding. Weathering of feldspars can produce clay minerals and dissolved silica, which affects downstream handling. In some terrains, deep chemical weathering of granite produces saprolite (decomposed but unconsolidated granite), which must be distinguished from intact fresh rock during excavation and processing.
The term "felsic" is essential in exploration and resource classification because it predicts both rock strength and mineral associations. Felsic intrusions often mark favorable ground for certain deposit types. In mine geology, recognizing felsic versus mafic country rock guides drilling depth, blast design, and water management strategy during extraction.