feldspar - Feldspar - Mineralogy, Crystallography, Structure: Sanidine and orthoclase are monoclinic or nearly so; the plagioclase feldspars are triclinic. All, however, have the same fundamental structure: it consists of a continuous, negatively charged, three-dimensional framework that is made up of corner-sharing SiO4 and AlO4 tetrahedrons (each …
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