Perthite is a variety of orthoclase felspar or microcline in which small veinlets of plagioclase felspar (albite) are present. It is a common mineral in rocks such as granite and syenite. A parallel to subparallel intergrowth of potassium and sodium feldspar; the potassium-rich phase is usually the host from which the sodium-rich phase evolves. K-feldspar with inclusions of plagioclase, formed by exsolution of the albite solid solution in K-feldspar
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