A type of sedimentary rock composed of a mixture of sand, silt, and clay, often with a significant amount of matrix material.
The geologist examined the wacke to determine its mineral composition.
A poorly sorted, matrix-supported sandstone containing more than about 15 % clay or silt-sized material, classified as a type of greywacke in sedimentary-rock schemes.
Core analysis revealed the reservoir layer to be a feldspathic wacke rich in clay matrix.