feldspars

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feldspars The most important group of rock-forming silicate minerals, including the alkali feldspars KAlSi3O8 to NaAlSi3O8 (K-feldspar to albite) and the plagioclase feldspars NaAlSi3O8 to CaAl2Si2O8 ( albite to anorthite). The potassium, sodium, and calcium end-members can be taken to represent the three apices of an equilateral triangle into which all the alkali feldspars and the plagioclase feldspars can be plotted (usually with the plagioclase feldspars along the base of the triangle and the alkali feldspars along the left-hand side).

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