Potassium feldspar refers to a number of minerals in the feldspar group that contain large amounts of potassium in the crystal lattice. Orthoclase (endmember formula KAlSi3O8), an important tectosilicate mineral that forms igneous rock Microcline, chemically the same as orthoclase, but with a different crystalline structure Sanidine, the high-temperature form of potassium feldspar Adularia, a more ordered low-temperature variety of orthoclase or partially disordered microcline Amazonite (sometimes called "Amazon stone"), a green variety of microcline