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.
McGraw-Hill Dictionary of Scientific & Technical Terms, 6E, Copyright © 2003 by The McGraw-Hill Companies, Inc.
The following article is from The Great Soviet Encyclopedia (1979). It might be outdated or ideologically biased.

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.

The Great Soviet Encyclopedia, 3rd Edition (1970-1979). © 2010 The Gale Group, Inc. All rights reserved.
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