lithic graywacke

lithic graywacke

[′lith·ik ′grā‚wak·ə]
(petrology)
A low-grade graywacke, that is, containing an abundance of unstable materials, especially a sandstone containing less than 75% quartz and chert, 15-75% detrital clay matrix, and more rock fragments than feldspar grains.
McGraw-Hill Dictionary of Scientific & Technical Terms, 6E, Copyright © 2003 by The McGraw-Hill Companies, Inc.