Feldspar
Feldspar, or Felspar, any of several minerals that together make up about half of the earth's crust. They are anhydrous aluminum silicates—that is, compounds of aluminum, silicon, and oxygen that do not contain water. Feldspars contain varying quantities of other elements, usually potassium, sodium, and calcium. Sometimes barium and other elements are also present.
Feldspar weathers to form clay, particularly kaolin. In the process, the potassium, sodium, and calcium it contains are released. Potassium from weathered feldspar is an important plant fertilizer.
Feldspar is used commercially in the manufacture of glass, pottery, and other ceramic materials. It is also used as an abrasive in some types of soap; as a binder in abrasive wheels; and as a filler material in paint and plastics. Some feldspars, including moonstone, are gemstones.
Most feldspar for commercial use is obtained from a type of rock called pegmatite. Italy and the United States are the world's leading producers.