An Etymological Dictionary of Astronomy and Astrophysics

A group of rock-forming minerals whose members are the most abundant constituents of igneous rocks. They consist of aluminum silicates of potassium, sodium, and calcium and
typically occur as colorless or pale-colored crystals.

See also: Modification of obsolete Ger. Feldspath (now Feldspat), from Ger. Feld “field” + obsolete Ger. Spath (now Spat) “spar.”