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graywacke

or grey·wacke

[grey-wak, -wak-uh]
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noun
  1. Geology. a dark-gray coarse-grained wacke.

Origin of graywacke

1805–15; partly translation, partly adapted from German Grauwache; see wacke
Dictionary.com Unabridged Based on the Random House Unabridged Dictionary, © Random House, Inc. 2018

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graywacke in Science

graywacke

[grāwăk′, -wăk′ə]
  1. Any of various dark gray, coarse-grained sandstones that contain abundant feldspar and rock fragments and often have a clay-rich matrix. Graywackes are thought to originate in environments where erosion, transportation, and deposition happen so quickly that minerals and rock fragments do not have sufficient time to break down into finer constituents.
The American Heritage® Science Dictionary Copyright © 2011. Published by Houghton Mifflin Harcourt Publishing Company. All rights reserved.