Potassium feldspar (pronounced: feld-spar)

Potassium feldspar is a common member of the the feldspar group of minerals. It contains potassium ions (K) in its silicate structure.

Also known as K-spar, or orthoclase this mineral is usually light cream to a salmon pink in color. Although color is usually a good indicator of some minerals, it should not be used as the basis for identification in most cases. Most pink feldspars are potassium feldspars though. A good way to distinguish between potassium feldspar and plagioclase is to look for striations. Striations are found on many clevage planes of plagioclase feldspar, but are not present on potassium feldspar.

Information provided by Patrick M. Colgan, Northeastern University
http://www.casdn.neu.edu