Any of a group of aluminosilicate (containing aluminum and silicon) minerals that also contains calcium, sodium, or potassium. Feldspars are the most common minerals in the Earth's crust and are the major component in nearly all igneous rocks found on the Earth, on the Moon, and in some meteorites. They also are common in metamorphic and some sedimentary rocks. Their complex chemical and structural properties make them useful for interpreting the origins of rocks. Natural feldspars can be divided into alkali and plagioclase feldspars.