gray·wacke (gr  w k , -wk )n. Any of various dark gray sandstones that contain shale. [Partial translation of German Grauwacke : grau, gray + Wacke, rock (from Middle High German, from Old High German waggo, boulder; see wegh- in Indo-European roots).] |
| graywacke (grwk, -wk) 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. |
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