similar igneous rocks (granitoids, diorites, gabbros) and in metamorphic gneisses similar to granite in composition. It can also occur in mylonites, in anorthosites and the orthopyroxene-bearing charnockites. Formation These characteristic intergrowths have been explained in a variety of ways: One explanation is Castle & Lindsley's exsolution silica-pump model. Accordingly, the texture was created as plagioclase formed by exsolution from alkali feldspar during cooling, under conditions in which silicon was mobile in the rock. The process does not require that magma be present during myrmekite formation. L.G. Collins explains the formation of myrmekite by: the K-metasomatic replacement of deformed primary plagioclase by secondary K-feldspar different varieties of Ca- and Na-Ca-metasomatism acting mainly upon deformed primary alkali feldspar, an exception being the replacement of deformed plagioclase in anorthosite. See also Granophyre Rock microstructure Granite Eutectic Solidus Symplectite References Minerals Petrology