Feldspar

n. [Ger. feldspath, from feld, field, and spath, spar.] (Min.) A mineral occurring in crystals and crystalline masses, somewhat vitreous in luster, and breaking rather easily in two directions, with smooth surfaces. The colors are usually white or flesh-red, occasionally bluish or greenish. It consists of silica, alumina, and potash. Feldspar is one of the essential constituents of granite, gneiss, mica-slate, and porphyry, and enters into the constitution of nearly all volcanic rocks.

The term feldspar family is applied to a group of allied minerals, including, besides common feldspar, the species albite, anorthite, labradorite, and ryacolite.