micropegmatite

micropegmatite

      quartz and alkali feldspar intergrowth so fine that it can be resolved only under the microscope; it is otherwise indistinguishable from the coarser intergrowths known as graphic granite. The quartz-feldspar interfaces are planar, and the quartz areas tend to be triangular in cross section. These patches of quartz are in parallel optical orientation, and it was long supposed that they were actually continuous, either above or below the plane of observation; a detailed study of the coarser intergrowths common in many pegmatites indicated, however, that the various quartz patches usually are separate individuals. Both the angular (runic, or letterlike) character of the quartz areas and their optical parallelism are evidently crystallographic responses to growth conditions.

      Micropegmatite often occurs in granite and diabase and composes all or a large part of granophyre. Where the intergrowth is coarse enough and sufficiently abundant to permit chemical analysis, the bulk composition averages about 25 percent quartz and 75 percent feldspar. This composition often is that of granites and rhyolites. In diabase, micropegmatite may be interstitial, forming pods (roughly cylindrical cigar-shaped aggregates), seams, or veins.

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Universalium. 2010.

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  • Micropegmatite — Mi cro*peg ma*tite, n. [Micro + pegmatite.] (Min.) A rock showing under the microscope the structure of a graphic granite (pegmatite). {Mi cro*peg ma*tit ic}, a. [1913 Webster] …   The Collaborative International Dictionary of English

  • micropegmatite — mi·cro·pegmatite …   English syllables

  • micropegmatite — …   Useful english dictionary

  • Micropegmatitic — Micropegmatite Mi cro*peg ma*tite, n. [Micro + pegmatite.] (Min.) A rock showing under the microscope the structure of a graphic granite (pegmatite). {Mi cro*peg ma*tit ic}, a. [1913 Webster] …   The Collaborative International Dictionary of English

  • micropegmatitic — adjective see micropegmatite * * * micropegmatitic / titˈik/ adjective • • • Main Entry: ↑micropegmatite …   Useful english dictionary

  • Micrographic texture — In petrology, micrographic texture is a fine grained intergrowth of quartz and alkali feldspar, interpreted as the last product of crystallization in some igneous rocks which contain high or moderately high percentages of silica. Micropegmatite… …   Wikipedia

  • granophyre — granophyric /gran euh fir ik/, adj. /gran euh fuyeur /, n. a fine grained or porphyritic granitic rock with a micrographic intergrowth of the minerals of the groundmass. [1880 85; GRANO + PHYRE] * * * ▪ rock       fine grained igneous rock that… …   Universalium

  • SILICE — Le dioxyde de silicium ou silice occupe, parmi les oxydes, une place exceptionnelle; en effet, par ses propriétés cristallochimiques, par ses modes de genèse, par son importance pétrographique, il s’apparente étroitement aux silicates. Dans la… …   Encyclopédie Universelle

  • μικροπηγματίτης — ο (πετρογρ.) σύμφυση ενός κρυστάλλου αλκαλικού αστρίου με έναν κρύσταλλο χαλαζία, η οποία έχει τόσο μικρό μέγεθος ώστε να είναι ορατή μόνο με το μικροσκόπιο. [ΕΤΥΜΟΛ. Αντιδάνεια λ., πρβλ. αγγλ. micropegmatite (βλ. μικρ[ο] )] …   Dictionary of Greek

  • quartz-dolerite — A variety of dolerite which contains interstitial quartz usually intergrown graphically with feldspar, forming patches of micropegmatite. A dyke rock of worldwide distribution, well represented by the Whin Sill rock in N. England …   Dictionary of automotive terms

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