Facts about Gneiss
In 2003, a team from the Smithsonian Institute collected a four-tonne boulder of Acasta Gneiss for display outside the National Museum of the American Indian in Washington, DC.
The term gneissose is used to describe rocks with properties similar to gneiss.
Orthogneiss designates a gneiss derived from an igneous rock, and paragneiss is one from a sedimentary rock.
Gneiss is formed by high-grade regional metamorphic processes from formations that were formerly either igneous or sedimentary rocks.
Gneisses that are formed by metamorphism of igneous rocks such as granite or diorite are termed granite gneisses, diorite gneisses, and so forth.
Gneiss resembles granite, except that the minerals are arranged into bands.
The study of gneiss has helped scientists understand the geological processes by which this metamorphic rock can be formed.
Gneissic rocks usually have medium to coarse foliation (aligned by directed pressure) and are largely recrystallized.
Sometimes it is difficult to tell the difference between gneiss and a schist because some gneiss appears to have more mica than it really does.
Augen gneiss (from the German augen, meaning "eyes") is a coarse-grained gneiss, interpreted as resulting from metamorphism of granite.