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An argillaceous sandstone characterized by an abundance of unstable mineral and rock fragments and a fine-grained clay matrix binding the larger, sand-size detrital fragments.



a rock of sedimentary origin consisting of small fragments (grains) of sedimentary and chiefly metamorphic and igneous rock with an admixture of fragments of basic volcanic rock and tufogenic material. A significant quantity of cementing material is characteristic. The color is usually dark gray, black, or dark green (owing to the chlorite in the cement). The fragmentary grains in the graywacke are angular or slightly rounded and are poorly sorted. Graywackes are typical for geosynclinal areas where they form thick strata originating during periods of the rapid accumulation of disintegration products from internal uplifts composed of more ancient rock.

References in periodicals archive ?
9 and 18 successfully scaled their spontaneous imbibition water-air experiments in sandstone, chalk, and Graywacke rock samples.
They consist of clay schists, graywacke and secondary conglomerates of Lower Carboniferous age.
The property is dominated by Jurassic Laberge group argillite, graywacke, siltstone, limestone and conglomerate, which are underlain by Triassic Stuhini group volcanics and carbonate.
of Rangin (1982), or Morro Hermoso Member] crossed by diabase dykes, with an interbedded sedimentary unit containing a Tithonian fauna in their upper part (Rangin, 1982); (ii) a 2500 m thick sequence of graywacke, claystone and conglomerate with poorly rounded volcanic pebbles, interbedded calcareous strata and pyroclastic deposits and, in its lower part, some interbedded basalt flows establishing its continuity with the underlying Morro Hermoso Member.