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Definition: arkose from The Penguin English Dictionary

a coarse-grained sandstone containing a high proportion of feldspar fragments in addition to quartz, derived from the rapid disintegration of granite or gneiss

arkosic adj [French arkose prob from Greek archaios ancient].


Summary Article: Arkose from Rock and Gem

A RELATIVELY COARSE SANDSTONE, arkose consists primarily of quartz and feldspar grains with small amounts of mica. It has a high feldspar content (more than 25 per cent of the sand grains), setting it apart from other sandstones. Its grains tend to be moderately well sorted, angular or slightly rounded, and usually cemented with calcite, although they can sometimes be cemented with iron oxides or silica. Arkoses are presumed to derive from granites and, like them, are pink or gray. Sandstones with a feldspar content of 5–25 per cent are called subarkoses.

  • Properties
  • Rock type Terrestrial, marine, or freshwater detrital, sedimentary
  • Fossils Rare
  • Major minerals Quartz, feldspar
  • Minor minerals Mica
  • Color Pinkish to pale gray
  • Texture Medium, angular

Sediments

These Torridonian sediments containing arkose were deposited in north-west Scotland.

Thin section

This medium-grained feldspathic red sand-stone is from Pre-cambrian sediments at Stoer, Scotland.

© 2008 Dorling Kindersley Limited

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