noun Download 🔗Share 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. Examples : "Many granite countertops are made up of quartz, mica, and feldspars. " geology mineral material science Chat with AIVocabulary GamePractice Reading