1. Plural of graywacke; a type of coarse-grained sedimentary rock composed of angular fragments of quartz, feldspar, and other minerals in a fine-grained matrix.
Usage: geology; also spelled greywacke

Examples

• The mountain range is composed primarily of graywackes and shales.
• Geologists identified graywackes in the rock samples collected from the riverbed.
• These graywackes formed from the rapid deposition of sediment in ancient marine environments.
• The graywackes in this region show evidence of significant tectonic activity.
• Quarries in the area extract graywackes for use as aggregate in construction.