greywacke
greywacke[ˈgreɪwakə](美 graywacke)noun- [mass noun](Geology)a dark coarse-grained sandstone containing more than 15 per cent clay
(地质)杂砂岩
语源- late 18th cent. (as grauwacke): from German Grauwacke, from grau 'grey' + wacke. The Anglicized form dates from the early 19th cent
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