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gneiss |
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gneiss (nīs), coarse-grained, imperfectly foliated, or layered, metamorphic rock rock, aggregation of solid matter composed of one or more of the minerals forming the earth's crust. The scientific study of rocks is called petrology. Rocks are commonly divided, according to their origin, into three major classes—igneous, sedimentary, and ..... Click the link for more information. . Gneiss is characterized by alternating light and dark bands differing in mineral composition and having coarser grains than those of schist. The light bands of gneiss are generally composed of quartz quartz, one of the commonest of all rock-forming minerals and one of the most important constituents of the earth's crust. Chemically, it is silicon dioxide, SiO2. ..... Click the link for more information. and feldspar feldspar (fĕl`spär, fĕld`–) or felspar ..... Click the link for more information. . Hornblende, biotite mica, garnet, or graphite commonly form the dark bands. Gneisses result from the metamorphism of many igneous or sedimentary rocks, and are the most common types of rocks found in Precambrian regions. Gneiss is found in New England, the Piedmont, the Adirondacks, and the Rocky Mts. Some gneisses are used as facing stone on buildings. gneissMedium- to coarse-grained metamorphic rock with parallel, somewhat irregular banding that has little tendency to split along planes. Gneiss is the principal rock over extensive metamorphic terrains. Orthogneiss is formed by the metamorphism of igneous rocks; paragneiss results from the metamorphism of original sedimentary rocks. Pencil gneiss contains rod-shaped individual minerals or segregations of minerals, and augen gneiss contains large lenticular mineral grains or mineral aggregates having the appearance of eyes scattered through the rock. gneiss any coarse-grained metamorphic rock that is banded and foliated: represents the last stage in the metamorphism of rocks before melting |
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Butler granite is a grey gneissic granite that was used for the steps and landings of the four exterior porticos of the Legislative Building (Figs. The altered and deformed host appears to be a gneissic to schistose intermediate to felsic intrusive but some deformed meta-volcanics are also present. A segment on gneissic host rocks begins with the Rottenstone deposit, continues with the Gordon-Werner Lake area and ends with the Namew Lake deposit. |
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