Aphanite

Aphanite (from the Greek αφανης, invisible) is a name given to certain typically dark-coloured igneous rocks which are so fine-grained that their component mineral crystals are not detected by the unaided eye. This texture results from rapid cooling in volcanic or hypabyssal (shallow subsurface) environments.

Aphanites are commonly porphyritic, having large crystals embedded in the fine groundmass or matrix. The large inclusions are called phenocrysts.

They consist essentially of plagioclase feldspar, with hornblende or augite, and may contain also biotite, quartz and a limited amount of orthoclase. Although a few authorities still recognize the aphanites as a distinct class, most systematic petrologists have discarded it, and regard these rocks as merely textural varieties of other species. The term is used as a field name pending laboratory identification. Hence, although typically an igneous term, any rock (sedimentary, igneous, or metamorphic) which is compact, crystalline and too fine-grained for its constituents to be identifiable in hand sample, is frequently said to be "aphanitic", without implying exactly to which of the principal rock groups it really belongs.

Common aphanites

*Andesite
*Basalt
*Basanite
*Dacite
*Felsite
*Leucitophyre
*Phonolite
*Rhyolite
*Trachyte

References

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Look at other dictionaries:

  • Aphanite — Aph a*nite, n. [Gr. ? invisible; a priv. + ? to appear.] (Min.) A very compact, dark colored ?ock, consisting of hornblende, or pyroxene, and feldspar, but neither of them in perceptible grains. [1913 Webster] …   The Collaborative International Dictionary of English

  • aphanite — [af′ə nīt΄] n. [Gr aphanēs, invisible < a , not + base of phainein, to appear (see FANTASY) + ITE1] rock so closely grained that its individual crystals cannot be seen by the unaided eye aphanitic [af′ənit′ik] adj …   English World dictionary

  • Aphanite — L aphanite est une roche magmatique dont la structure est à grain très fin. Les cristaux qui la composent sont si petits qu ils ne peuvent être observés à l œil nu. L aphanite était utilisée par les artisans du Néolithique pour fabriquer des… …   Wikipédia en Français

  • aphanite — aphanitic /af euh nit ik/, adj. /af euh nuyt /, n. Petrog. a fine grained igneous rock having such compact texture that the constituent minerals cannot be detected with the naked eye. [1860 65; < Gk aphan(és) unseen, hidden, invisible (a A 6 +… …   Universalium

  • aphanite — noun Certain dark igneous rocks having grain so fine that the individual crystals cannot be seen with the naked eye …   Wiktionary

  • aphanite — (a fa ni t ) s. f. Terme de géologie. Sorte de roche. ÉTYMOLOGIE    Terme grec signifiant non apparent, à cause que les parties fondues de cette roche ne se laissent pas reconnaître à l oeil …   Dictionnaire de la Langue Française d'Émile Littré

  • aphanite — n. type of fine grained rock …   English contemporary dictionary

  • aphanite — aph·a·nite …   English syllables

  • aphanite — /ˈæfənaɪt/ (say afuhnuyt) noun any fine grained igneous rock having such compact texture that the constituent minerals cannot be detected with the naked eye. {Greek aphanēs obscure + ite1} –aphanitic /æfəˈnɪtɪk/ (say afuh nitik), adjective …   Australian English dictionary

  • aphanite — noun fine grained homogeneous rock (such as basalt) containing minerals undetectable by the naked eye • Derivationally related forms: ↑aphanitic • Hypernyms: ↑rock, ↑stone …   Useful english dictionary


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