Sanidine is the high temperature form of potassium feldspar Sanidine is found most typically in felsic volcanic rocks and trachyte crystal system. Orthoclase polymorph stable at lower temperatures. At yet lower temperatures, microcline polymorph of potassium feldspar, is stable.
Due to the high temperature and rapid quenching, sanidine can contain more sodium in its structure than the two polymorphs that equilibrated at lower temperatures. Sanidine and high albite constitute a solid solution series with intermediate compositions termed anorthoclase. Exsolution of an albite phase does occur; resulting cryptoperthite can best be observed in electron microprobe images.