Mica-schists sentence example

  • The Silurian mica-schists of Bergen in Norway are fossiliferous; in the Alps it is believed that even Mesozoic rocks pass laterally into mica-schists and talc-schists.
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  • In the mica-schists of this group biotite or muscovite may be the principal mineral and often both are present in varying proportions; the mica has developed from the argillaceous matter of the original rock; in addition there is always quartz and sometimes felspar (albite or oligoclase).
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  • The phyllites (q.v.) form a middle term between this group and the slates; they consist usually of quartz, white mica and chlorite, and have much of the foliation and schistosity of the mica-schists.
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  • The orthoschists are white mica-schists produced by the shearing of acid rocks, such as felsite and porphyry.
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  • They are soft and lustrous, with a peculiarly smooth feel, and though often confounded with mica-schists may be distinguished by their richness in magnesia; many of them contain tremolite or actinolite; others have residual grains of olivine or augite; and here also every gradation can be found between the unmodified igneous types and the perfectly metamorphic schists.
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  • The oldest rocks, consisting of slate, mica-schists and grits, which have been correlated with the metamorphic series of the eastern Highlands, form an incomplete ring round the granite in the north of the island and occupy the whole of the west coast from Loch Ranza south to Dougrie.
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  • Copper pyrites occur at Falun in mica-schists, surrounded by halleflinta.
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  • They come out as mica-schists under the Carboniferous sandstones of northern Antrim, and disappear southward under the basaltic plateaux.
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  • The oldest rocks in this large area are a stratified series of mica-schists, limestones and quartzites, with numerous intrusive sheets of diorite, the whole having been metamorphosed by pressure, with frequent overfolding.
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  • They are often contorted, and near the contact with the granite pass into mica-schists and quartzites.
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  • The sedimentary schists or paraschists have three great subdivisions, the mica-schists and chlorite-schists (which correspond in a general way to shales or clay rocks) the calc-schists (impure limestones) and the quartz-schists (metamorphosed sandstones).
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