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Consisting of three end members: potassium feldspar (K-spar, KAlSi3O8), plagioclase with calcium (CaAl2Si2O8, called anorthite), and plagioclase with sodium (NaAlSi3O8, called albite). Commonly blocky, with two cleavages as ~90°. Plagioclase is typically more dull white and grey, and K-spar is more vibrant white, orange, or red. The most common mineral found within the crust, and a major component of almost all igneous rocks, some sedimentary rocks, and some metamorphic rocks. Structure is a three-dimensional framework of silica tetrahedra, with locations open for cations (K, Na, Ca).

kspar, k-spar, plag, plagioclase
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Author: Chris

Assistant Professor, Salt Lake Community College, Salt Lake City, Utah