/gray"wak', -wak'euh/, n.
Geol. a dark-gray coarse-grained wacke.
Also, greywacke.
[1805-15; partly trans., partly adapted from G Grauwache; see WACKE]

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or dirty sandstone

Sedimentary rock composed of sand-sized grains in a fine-grained clay matrix.

The sand-sized grains frequently include rock fragments of wide-ranging mineralogies (e.g., pyroxenes, amphiboles, feldspars, and quartz). The clay matrix may constitute up to 50% of the volume. Of the clay minerals, chlorite and biotite are most abundant. The matrix tends to bind the grains strongly and form a relatively hard rock.

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Universalium. 2010.

Look at other dictionaries:

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  • graywacke — [grā′wak΄] n. [partial transl. of Ger grauwacke: see GRAY1 &] 1. a nonporous, dark colored sandstone containing angular particles of other rocks 2. a fine grained conglomerate resembling sandstone …   English World dictionary

  • graywacke — noun Etymology: partial translation of German Grauwacke Date: 1811 a coarse usually dark gray sandstone or fine grained conglomerate composed of firmly cemented fragments (as of quartz or feldspar) …   New Collegiate Dictionary

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