The Collaborative International Dictionary
Graywacke
Graywacke \Gray"wacke`\, n. [G. grauwacke; grau gray + wacke wacke. See Gray, and Wacke, and cf. Grauwacke.] (Geol.) A conglomerate or grit rock, consisting of rounded pebbles and sand firmly united together.
Note: This term, derived from the grauwacke of German miners, was formerly applied in geology to different grits and slates of the Silurian series; but it is now seldom used.
Wiktionary
graywacke
n. (alternative form of greywacke English)
Usage examples of "graywacke".
Isle of Man, perhaps three quarters, consists of a barren soil overlaid upon graywacke slate and on clay slate.