felsica

Felsica is a term used in geology as a hypothetical mineral that would represent a major constituent of felsic rocks. It is not an officially recognized mineral name; rather, it serves as a teaching concept to illustrate the properties and classification of silica- and feldspar-rich rocks, such as granites and rhyolites.

In composition, felsica would be dominated by silica (SiO2) and light-colored silicate minerals, mainly alkali feldspar (orthoclase and microcline) and quartz, with plagioclase present in smaller amounts. Accessory minerals such as muscovite or minor biotite could occur, while ferromagnesian minerals would be rare.

Physical properties would include a light color range from white to pink, a vitreous to pearly luster, and a hardness around 6 to 7 on the Mohs scale. The material would typically have a low to moderate density, approximately 2.6 to 2.8 g/cm3, and display feldspar cleavage with less pronounced quartz fracture.

Geologically, felsica is imagined to form in the continental crust through fractional crystallization of granitic magmas or during late-stage differentiation of felsic systems. It would commonly occur in granitoids, granitic pegmatites, and associated silicic intrusions.

Although not an official mineral name, felsica is used pedagogically to discuss felsic rock classification, mineral balance, and petrogenesis. The concept helps describe how silica-rich, feldspar-dominated rocks contrast with intermediate and mafic compositions.