Graywacke

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graywacke

[′grā‚wak·ə]
(petrology)
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.

Graywacke

 

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 ?
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.
Descripcion: Constituida por interestratificaciones de lutitas y areniscas (areniscas y graywackes liticas), con laminacion paralela, cruzada, bidireccional, posibles briozooarios y globigerinoides, con fuerte influencia volcanica (clastos de rocas volcanicas: 3-70%, mayoritariamente alrededor de un 60%).
Pyrargyrite probably does not occur in the Llallagua stock, but it was an ore mineral with galena in a peripheral vein in graywackes at Uncia, 3 km south of the intrusion.
This fault dips approximately 35 degrees to the northeast, and brings the Mesozoic sediments and Tertiary volcanics into contact with older, underlying shales, graywackes and mafic volcanic rocks.
1) could be summarized as a basement of Upper Precambrian age which crops out in the center of the Olivenza-Monesterio anticlinorium, formed by successive levels of schists, graywackes, shales and graphitic quartzites affected by a low-grade regional metamorphism (Benito et al.
The rocks exposed at the Hale Creek mine are typical of the Franciscan-Knoxville group of late Jurassic age and consist of sandstones, shales, cherts, greenstones and graywackes.