Felsic

In geology, felsic is a modifier describing igneous rocks that are relatively rich in elements that form feldspar and quartz.

Felsic refers to silicate minerals, magma, and rocks which are enriched in the lighter elements such as silicon, oxygen, aluminium, sodium, and potassium.

Although this intuition makes sense from an acid-base perspective in aquatic chemistry considering water-rock interactions and silica dissolution, siliceous rocks are not formed by this protonated monomeric species, but by a tridimensional network of SiO44– tetrahedra connected to each other.

Felsite is a petrologic field term used to refer to very fine-grained or aphanitic, light-colored volcanic rocks which might be later reclassified after a more detailed microscopic or chemical analysis.

If the rock is analyzed and found to be felsic but is metamorphic and has no definite volcanic protolith, it may be sufficient to simply call it a 'felsic schist'.

A felsic volcanic lithic fragment , as seen in a petrographic microscope . Scale box is in millimeters.
Close-up of granite from Yosemite National Park .
A specimen of rhyolite .