1. A hard, coarse-grained sedimentary rock composed of angular fragments of quartz, feldspar, and other minerals in a fine-grained matrix, typically formed from the rapid deposition of sediment in deep water.
Usage: geology; also spelled 'graywacke' in U.S. English

Examples

• The cliff face exposed layers of greywacke dating back millions of years.
• Geologists identified the greywacke formation as evidence of ancient turbidity currents.
• The greywacke samples collected from the riverbed contained fragments of various minerals.
• This greywacke deposit is commonly found in mountain ranges formed by tectonic activity.
• The dark greywacke rock was difficult to cut due to its hardness and coarse texture.