Feldspar is the name of a group of rock-forming tectosilicate minerals that make up as much as 60% of the Earth's crust.
Feldspar forms crystals from magma in both intrusive and extrusive rocks, and they can also happen as compact minerals, as veins, and are also present in many types of metamorphic rock. Rock formed entirely of plagioclase feldspar is known as anorthosite. Feldspar is also found in many types of sedimentary rock.