Sentence Examples


  • In all of them there is at least one mineral which crystallizes in platy forms (e.g.
  • The platy minerals have also a perfect cleavage parallel to their flat surfaces, while the fibrous species often have two or more cleavages following their long axes; hence a schistose rock may split not only by separation of the mineral plates from one another but also by cleavage of the parallel minerals through their substance.
  • The difference between schists and gneisses is mainly that the latter have less highly developed foliation; they also, as a rule, are more coarse grained, and contain far more quartz and felspar, two minerals which rarely assume platy or acicular forms, and hence do not lead to the production of a fissile character in the rocks in which they are important constituents.
  • Micas and other platy minerals (such as chlorite), which naturally grow most rapidly on their edges, would show this tendency best, and such minerals usually form a large part of the best slates; but even Sketch (by Du Noyer) of a block of variegated slate from Devil's Glen, Co.
  • These are overlaid conformably by a thick series of platy limestones, known as the Viglas limestone, which appears to represent the rest of the Jurassic system and also the lower part of the Cretaceous.

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