(1) Any of a group of hard crystalline minerals that consist of aluminum silicates of potassium or sodium or calcium or barium
Feld, field + Spath, spar
- Any of a large group of rock-forming minerals that, together, make up about 60% of the earth's outer crust. The feldspars are all aluminum silicates of the alkali metals sodium, potassium, calcium and barium. Feldspars are the principal constituents of igneous and plutonic rocks.