General petrological term applied to coarse-grained, banded rocks that formed during high-grade regional metamorphism. The banding (gneissose banding, or gneissosity) is a result of the separation of dark minerals (e.g. biotite, hornblende, and pyroxenes) and the light-coloured quartzofeldspathic minerals. A gneissose rock may be described more strictly by adding a qualifying prefix, e.g. biotite gneiss, hornblende gneiss, or pelitic gneiss.