Learn how to say Graywacke correctly in English with this tutorial pronunciation video.
Oxford dictionary definition of the word greywacke:
[mass noun] Geology
a dark coarse-grained sandstone containing more than 15 per cent clay:
a 120-foot pyramid of battered greywacke a quarter mile offshore
the shales and greywackes of the Skiddaw Group
late 18th century (as grauwacke): from German Grauwacke, from grau ‘grey’ + wacke. The anglicized form dates from the early 19th century