Gneiss rocks are metamorphic rocks that have been altered chemically from existing rocks into a denser type of rock. Compression, plate tectonics, stress and shearing warp and change existing rocks over time. Gneiss is granite that has been changed by these forces into denser rock.
Gneiss is a coarse-grained rock that characteristically shows banding between layers, which is created by high temperatures and high pressure. The bands separate different types of material as they were compressed together by natural forces. Colors range from shades of gray to pink, but with layers of darker material. Gneiss rocks formed from igneous type rock are called orthogneisses. Those that are formed from sedimentary type rock are called paragneisses. The origin of the word gneiss is disputed. It may come from the Middle High German, gneist, meaning “to spark” because the rock glitters, but other sources believe it comes from and old Saxon mining term meaning decayed, rotten or worthless material.
Gneiss Rock Composition
Gneiss is composed of granite, shale and volcanic rock. It most often contains quartz, potassium feldspar and sodium feldspar, along with small amounts of biotite, muscovite, hornblende, shale or gabbro. Garnet, tourmaline and other crystalline materials may be incorporated into the rock. The banding comes from the segregation of light and dark silicate materials. The term “gneissic texture” is used to describe this segregation of material at temperatures around 600 to 700 centigrade. Though gneiss rock may have sparkling particles that appear to be mica, they are generally very low in this material.
Gneiss Rock Distribution
Gneiss rock is found in many mountainous areas where the natural forces of the Earth have produced the heat and pressure to create the conditions for its formation. The Rocky Mountains of the United States, as well as the Adirondack Mountains are examples of areas where this type of rock is found. Anywhere that volcanic action or the movement of the Earth’s tectonic plates has cause shifting of the crust is a likely place to find gneiss rock.
How Gneiss Rock Is Used.
Gneiss rock is varies in composition and appearance depending on the type of materials that are present when natural forces form the rock. It is a tough and hard rock, which makes it useful for many applications. Gneiss is used in building construction, road construction, flooring and ornamental stone. It is also frequently used for gravestones, stone for building facings and for solid work surfaces.
Gneiss rock is mined in many areas of the world. It makes a useful building material that lasts for years.