Ribbe, Paul H. Formerly, Department of Geological Sciences, Virginia Polytechnic Institute, Blacksburg, Virginia.
Last reviewed:April 2021
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- Chemical composition
- Crystal structures
- Alkali feldspars
- Plagioclase feldspars
- Mechanical properties
- Optical properties
- Melting properties
- Phase equilibria of the feldspar binary systems
- System KAISi3 O8 -CaAI2 Si2 O8
- System KAISi3 O8 -NaAISi3 O8
- System NaAISi3 O8 -CaAI2 Si2 O8
- Related Primary Literature
- Additional Reading
Any of a group of aluminosilicate minerals whose crystal structures are composed of corner-sharing [AlO4] and [SiO4] tetrahedra linked in an infinite three-dimensional array, with charge-balancing cations [primarily sodium (Na), potassium (K; Fig. 1), and calcium (Ca)] occupying large, irregular cavities in the framework of the tetrahedra. Collectively, the feldspars constitute about 60% of the outer 13–17 km (8–10 mi) of the Earth's crust. They are nearly ubiquitous igneous and metamorphic rocks, and are a primary constituent of arkosic sediments derived from them. The importance of the many feldspars that occur so widely in igneous, metamorphic, and some sedimentary rocks cannot be underestimated, especially from the viewpoint of a petrologist attempting to unravel earth history. See also: Arkose; Mineralogy; Petrology; Silicate minerals
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