Feldspars crystallize from magma as veins in both intrusive and extrusive igneous rocks and are also present in many types of metamorphic rock. Rock formed almost entirely of calcic plagioclase feldspar (see below) is known as anorthosite.Feldspars are also found in many types of sedimentary rocks.he name feldspar derives from the German Feldspat, a compound of the words Feld, field, and Spat, a rock that does not contain ore . The change from Spat to-spar was influenced by the English word spar, a synonym for mineral. Feldspathic refers to materials that contain feldspar.