other names: Gneus
mineral class: ?
chemical formula: SiO2 + various elements (including Al, Fe, Mg)
Chemical elements: Silicon, oxygen
Similar minerals: Granite
colour: depending on the composition
crystal structure: /
mass density: 2,8
magnetism: weak magnetic
Mohs hardness: about 3
stroke color: ?
use: Building material
General information about the gneiss:
Under the term gneiss different rock types are summarized, which have a feldspar proportion of at least twenty percent and show a characteristic parallel structure. The name gneiss comes from the Old and Middle High German and is derived from the words "gneisto" and "ganeist", which means "spark" or "sparkle" or "shimmer" mean. These names were used by the miners in the Erzgebirge, which probably referred to the shimmering percentage of mica in the gneiss. Until the 18th century, the term "gneus" was common in German-speaking countries.
Gneiss appears mainly in different shades of gray, but may also have greenish, pale pink or brownish tints. The rock owes its unmistakable appearance to the alternately light and dark as well as parallel arranged bands, which consist of different minerals. Due to the mica content, gneiss shimmers slightly silvery. The cracks appear much brighter than the surfaces and look almost smooth. The otherwise coarse-grained gneisses are mainly composed of quartz and feldspar, which provide the light bands in the rock. The dark parts are due to mineral admixtures, which may consist of pyrite, biotite, hornblende, epidodite, magnetite and garnets, among others. The composition of the gneiss, as with other rocks, depends on the environmental conditions that prevailed during its formation.
Origin and occurrence:
Gneisses are metamorphic rocks that form in the course of a melting of other rocks such as granite, sandstone, slate and other sedimentites. The recrystallization occurs under the action of high temperatures, which are about seven hundred degrees Celsius. The banding, which give gneisses their distinctive appearance, is due to the one-sided pressure conditions during crystallization.
Gneiss is mined as a versatile natural stone around the world. The countries in which economically important deposits are located include Germany, Austria and the Czech Republic, France, Portugal, Italy and Switzerland. Gneisses are being widely promoted in much of Britain, the United States, China, Australia, India and Brazil.
Use by humans:
Gneiss is considered a durable natural stone, which finds versatile application as a building material. Gneisses have a high density and are therefore very resilient. In addition, this natural stone is acid-resistant, frost-resistant and durable. This makes it interesting for the production of different components for indoor and outdoor use. Gneisses are used not only to make pavements and paving stones for roads and garden paths, but also stone floors, worktops and other elements for kitchens, bathrooms and living areas. Another use find gneisses in sculpture. The most famous work of art made of gneiss is the Mount Rushmore National Memorial in South Dakota, depicting the heads of four US Presidents Washington, Jefferson, Roosevelt and Lincoln.