Gneiss is a common and widely distributed rock type formed by high-grade regional metamorphism of either pre-existing igneous or sedimentary rocks. It is often foliated (composed of layers of sheet-like planar structures). The foliations are characterized by alternating darker and lighter colored bands, called “gneissic banding”. The biotite can clearly be seen in this example from Evje in Norway. Specimens are supplied in a polythene bag in lots of 1 kg with a label.
