Feldspar (German: Feldspat) pertains to the mineral found in granite which melts around 2300 fahrenheit, used as a flux in clay bodies and glazes.
When feldspar rock loses its alkaline content through decomposition it becomes kaolin which is the origin of clay.
One of a group of rock-forming minerals, the most abundant group in the Earth's crust. They are the chief constituents of igneous rock and are present in most metamorphic and sedimentary rocks. All feldspars contain silicon, aluminum, oxygen, linked together to form a framework; spaces within this structure are occupied by sodium, potassium, calcium, or occasionally barium, in various proportions.