arkose

arkosic, adj.
/ahr"kohs/, n.
a granular sedimentary rock composed of quartz and feldspar or mica; a feldspathic sandstone.
[1830-40; < F]

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Coarse sandstone that has formed by the disintegration of granite without appreciable decomposition.

It thus consists primarily of quartz and feldspar grains. In the absence of stratification, arkose may bear superficial resemblance to granite, and it sometimes has been described as reconstituted granite, or granite wash. Like the granite from which it was formed, arkose is pink or gray.

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      coarse sandstone (sedimentary rock composed of cemented grains 0.06–2 millimetres [0.0024–0.08 inch] in diameter) primarily made up of quartz and feldspar grains together with small amounts of mica, all moderately well sorted, slightly worn, and loosely cemented with calcite or, less commonly, iron oxides or silica. Arkose is often used informally by geologists as a feldspathic arenite, because it is rich in feldspar (more than 25 percent of the sand grains) and distinguished from graywacke by its lighter colour. In the absence of stratification, arkose may bear superficial resemblance to granite, and it aptly has been described as reconstituted granite, or granite wash. Like the granites from which they were formed, arkoses are pink or gray.

      The geological significance of arkose has been much debated. Under normal conditions most of the feldspar decomposes and is converted to clay minerals during weathering of the source rocks, whereas under conditions of extreme dryness or low temperatures, decomposition of the feldspar is inhibited or greatly retarded. Arkoses were, therefore, presumed to be derived from the erosion of a granitic terrane characterized by an arid or glacial climate. Now, however, it is known that the feldspar may escape destruction and thus be transported and deposited with quartz sands if rates of uplift, erosion, and deposition are great enough. Under such conditions, irrespective of the climate, weathering processes are incomplete and the sands derived from such terrane are high in feldspar content. Arkoses, therefore, may be said to indicate either a climatic extreme or high relief. Most ancient arkose deposits seem to be the product of high relief.

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Universalium. 2010.

Look at other dictionaries:

  • Arkose — (pronEng|ˈɑrkoʊz) is a detrital sedimentary rock, specifically a type of sandstone containing at least 25% feldspar.cite book author = Folk, R.L. year = 1974 title = Petrology of Sedimentary Rocks publisher = Hemphill isbn = 0 914696 14 9 url =… …   Wikipedia

  • arkose — ● arkose nom féminin Grès feldspathique, dérivant de l érosion de roches granitiques sédimentées et constitué de grains de quartz, feldspaths et micas. ⇒ARKOSE, subst. fém. GÉOL. Grès composé de quartz et de feldspath (contenant parfois du mica) …   Encyclopédie Universelle

  • Arkose — Ar*kose , n. [F] (Petrog) A sandstone derived from the disintegration of granite or gneiss, and characterized by feldspar fragments. {Ar*kos ic}, a. [Webster 1913 Suppl.] …   The Collaborative International Dictionary of English

  • Arkose — Arkose, ein im mittleren Frankreich, sowie im Rothliegenden Deutschlands vorkommender Sandstein, welcher neben Quarzkörnern viele Feldspathkörner u. Glimmerblättchen in einem thonigen Bindemittel enthält; häufig ist dieser A. dem Granit sehr… …   Pierer's Universal-Lexikon

  • Arkōse — Arkōse, feldspatreicher Sandstein, z. T. gebildet aus Granitgrus (regenerierter Granit), mit tonigem oder kieseligem Bindemittel, findet sich vielfach im Karbon, Rotliegenden, Buntsandstein etc …   Meyers Großes Konversations-Lexikon

  • arkose — [är′kōs΄, är kōs′] n. [Fr] a medium grained sandstone containing feldspar, derived from the erosion of igneous rock, esp. granite …   English World dictionary

  • Arkose — Exemple d utilisation d arkose pour la construction d une église en Auvergne. L arkose est une roche sédimentaire détritique terrigène composée de quartz (jusqu à 60 %), de feldspath (au moins 25 %), souvent de quelques micas et d un… …   Wikipédia en Français

  • Arkose — Relativ dunkle Arkose; Fundort: Bebertal in Sachsen Anhalt; Alter: Oberkarbon; Länge des Handstückes: ca. 6 cm Arkose bezeichnet eine Klasse von Sandsteinen, welche sich durch einen hohen Gehalt an Feldspat auszeichnet. Inhaltsverzeichnis …   Deutsch Wikipedia

  • Arkose — Ar|ko|se 〈f. 19; unz.; Geol.〉 Feldspat u. Glimmer enthaltendes Sedimentgestein * * * Arkose   [französisch] die, , Sandstein mit mehr als 25 % Feldspat; unter ariden Bedingungen aus feldspatreichen Gesteinen (Granit, Gneis) entstanden. * * *… …   Universal-Lexikon

  • arkose — noun Etymology: French Date: 1839 a sandstone characterized by feldspar fragments that is derived from granite or gneiss which has disintegrated rapidly • arkosic adjective …   New Collegiate Dictionary

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