Gneisses
Gneiss is a high-grade metamorphic rock characterized by pronounced foliation and distinct compositional banding, produced when minerals segregate into light and dark layers during metamorphism. The grains are typically coarse, reflecting prolonged recrystallization under elevated temperatures and pressures.
Most gneisses form from pre-existing rocks (the protoliths) such as granites, granodiorites, diorites, or sedimentary rocks
Minerals commonly found include quartz, feldspars, biotite, muscovite and amphiboles; the light bands are quartz and
Gneisses are widespread in the continental crust and are major components of many ancient metamorphic belts,