greywacke
/ˈgreɪˌwækə/( <美> graywacke)
noun
mass noun
- Geology a dark coarse-grained sandstone containing more than 15 per cent clay【地质】杂砂岩。
词源
late 18th cent. （as grauwacke）： from German Grauwacke, from grau 'grey' + WACKE. The Anglicized form dates from the early 19th cent.