greywacke

grey wacke ▶noun British spelling of graywacke.

greywacke

greywacke |ˈgreɪwakə |(US graywacke ) ▶noun [ mass noun ] Geology a dark coarse-grained sandstone containing more than 15 per cent clay. ORIGIN late 18th cent. (as grauwacke ): from German Grauwacke, from grau ‘grey ’ + wacke. The anglicized form dates from the early 19th cent.