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.
User Defined Definitions
"any of a group of hard crystalline minerals that consist of aluminum silicates of potassium or sodium or calcium or barium"