Paragneiss

a metamorphic rock formed in the earth’s crust from sedimentary rocks (sandstones and argillaceous schists) that recrystallized in the deep zones of the earth’s crust in an amphibolite facies of metamorphism. Paragneiss consists of quartz and feldspars with admixtures of other minerals, typically andalusite, sillimanite, disthen, staurolite, cordierite, and tourmaline. The varieties of paragneiss are distinguished according to the admixture content. A certain excess of alumina, caused by the content of clay material in the primary sediments, is typical of paragneiss. In contrast to paragneiss, orthogneiss is formed through transformation of magmatic rocks.