Gneiss is a banded coarse-grained metamorphic rock that formed deep in the crust beneath forming mountain ranges. The chemical composition may be highly variable, although most gneissose rocks are granitic.
It is characterized by foliation that generally looks like black and white banding. The name originated with Saxon miners in Germany.
Ortho gneiss is essentially metamorphosed granite, so it too is similar in appearance to granite. Ortho gneiss, however, can develop foliation strong enough to be recognized on aerial photographs by subtle banding and elongation of drainage in a direction parallel to foliation. Depending on the grade of metamorphism, gneiss derived from granite usually provides equivalent strength properties.
Para gneiss is a metasediment (high-grade metamorphism of a sedimentary rock); hence, it may retain some of the morphological characteristics of the original sediment from which it developed. Look for sharp, crested ridges, and angular drainage patterns which tend toward parallel. Para gneiss is common to belted metamorphics around the cores of plutons.
What are the uses for gneiss?
Metamorphic Gneiss has many uses as a building material such as Flooring, Ornamental stones, Gravestones, Facing stones on buildings and Work surfaces.
C.E. Glass;R. Roy;sandatlas