Potassium Feldspar (Microcline)
(c) 2002 Andrew Alden, licensed to About.com, Inc. (fair use policy)
Microcline is a potassium feldspar mineral. Unlike the plagioclase feldspar group, which varies in composition, potassium feldspar has the same formula, KAlSi3O8, but varies in crystal structure depending on the temperature it formed at. Microcline is the stable form of potassium feldspar below about 400° C.
In the field, workers generally just write down "K-spar" and leave it at that until they can get to the laboratory. But the deep green color of this mineral, the amazonite variety of microcline, makes it stand out in a pretty homogeneous field. The color is from the presence of lead.
Learn more about the feldspar minerals here.
See more feldspars in the feldspars picture gallery.
Fossils
Geologic Features and Processes
Glaciers and Ice
Landforms
Minerals
Rocks
Geology and Society
