1. Plural of greywacke; 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 'graywackes' in U.S. English

Examples

• The geologist identified several greywackes in the rock formation.
• Greywackes are commonly found in mountain ranges and ancient sedimentary basins.
• The dark greywackes indicated a turbidite depositional environment.
• These greywackes contain fragments of granite and metamorphic rocks.
• The sample of greywackes showed poor sorting and angular grains.