exfoliation


exfoliation
/eks foh'lee ay"sheuhn/, n.
1. the act, state, or process of exfoliating.
2. the state of being exfoliated.
3. something that is exfoliated or scaled off.
[1670-80; NL exfoliation- (s. of exfoliatio). See EXFOLIATE, -ION]

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 separation of successive thin shells, or spalls, from massive rock such as granite or basalt; it is common in regions that have moderate rainfall. The thickness of individual sheet or plate may be from a few millimetres to a few metres.

      Some geologists believe that exfoliation results when rocks formed at depth are exposed at the ground surface; the previous compressional forces would decrease and thus allow the rock to expand by fracturing parallel to the surface. Quite often, however, the fractures are not parallel to the ground surface, and this circumstance is taken as an indication of some other method of formation. Large daily variations in temperature, especially pronounced in deserts, were also credited with producing exfoliation—expansion from heating during the day followed by contraction from rapid cooling at night was thought to cause the separation of thin slabs from large blocks of rock at the surface. This view has been discredited by careful experiments using an electric heating and cooling device; thousands of alternations between temperatures considerably higher and lower than those measured in deserts have failed to produce in samples of rock any fractures detectable even under high magnification.

      Study of thin shells that separate from rock exposed to the weather reveals as a common cause of the separation the slow development of clay minerals, which involves an increase in volume. The outer surface of exposed rock dries rapidly after wetting; but moisture that penetrates into minor crevices stays until some decay is started, and the resultant swelling causes flaking roughly parallel to the outer rock surface.

      A small-scale form of exfoliation, called spheroidal weathering, is restricted to boulder-sized rock material and may occur at some depth within the Earth. In this case, rounded boulders are found surrounded by layers of disintegrated material.

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Universalium. 2010.

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  • exfoliation — [ ɛksfɔljasjɔ̃ ] n. f. • 1478; lat. exfoliatio ♦ Le fait de s exfolier; son résultat. Exfoliation de l écorce d un arbre. Lamelles qui se détachent par exfoliation (écailles, plaques). ♢ Méd. Élimination, sous forme de lamelles, de certaines… …   Encyclopédie Universelle

  • Exfoliation — has several meanings: * Exfoliation (botany) describes the loss of leaves (or, in some cases, pieces of bark) from a plant. * Exfoliation (cosmetology), is a cosmetic technique aimed at removing dead skin cells from the face and body. *… …   Wikipedia

  • Exfoliation — Ex*fo li*a tion, n. [Cf. F. exfoliation.] The scaling off of a bone, a rock, or a mineral, etc.; the state of being exfoliated. [1913 Webster] …   The Collaborative International Dictionary of English

  • Exfoliation — Exfoliation. См. Расслоение. (Источник: «Металлы и сплавы. Справочник.» Под редакцией Ю.П. Солнцева; НПО Профессионал , НПО Мир и семья ; Санкт Петербург, 2003 г.) …   Словарь металлургических терминов

  • Exfoliation — (v. lat.), Abblätterung; E. der Knochen, Abblätterung der Knochen, Trennung durch Brand (Nekrosis) abgestorbener, kleiner, blätteriger od. anderer Knochenstücke, als Heilproceß der Natur. Daher Exfoliations (Exfoliativ ) trepan, s.u. Trepan …   Pierer's Universal-Lexikon

  • Exfolĭation — (lat.), Abblätterung, Zerstörung von Organen, z. B. Knochen, so daß sich von denselben dünne, flächenhaft ausgedehnte Schichten abstoßen …   Meyers Großes Konversations-Lexikon

  • Exfoliation — (lat.), Abblätterung, Abschieferung der Knochen …   Kleines Konversations-Lexikon

  • Exfoliation — Exfoliation, lat., chirurg. Operation, bei welcher von einem harten Körper schichtenweise abgeschnitten wird …   Herders Conversations-Lexikon

  • Exfoliation —   [zu lateinisch folium »Blatt«, also eigentlich »Entblättern«] die, / en, spontane (unmerkliche) Abschilferung abgestorbener Deckzellen von Haut und Schleimhaut, krankhaft gesteigert bei entzündlichen Vorgängen und Tumoren. Die… …   Universal-Lexikon

  • exfoliation — early 15c., noun of action from L. exfoliare (see EXFOLIATE (Cf. exfoliate)) …   Etymology dictionary


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