Definition of "graywacke" [gray•wacke]

• Any of various dark gray sandstones that contain shale. (noun)

American Heritage(R) Dictionary of the English Language, Fifth Edition. Copyright (c) 2011 by Houghton Mifflin Harcourt Publishing Company. Published by Houghton Mifflin Harcourt Publishing Company. All rights reserved.

• "Ecoregion 66c is underlain by Precambrian metamorphic rock, including quartzite, graywacke, and conglomerate of the Lynchburg Formation."
• "Parts of the Danville Basin, on the other hand, are higher and have more relief than adjacent portions of the Piedmont because they are underlain by relatively resistant rocks including conglomerate and graywacke (Hack, 1982; Virginia Division of Mineral Resources, 1993)."
• "A fragment of an exquisitely carved graywacke vase proved there had been a royal presence -- such stone vessels were products of royal workshops in the early First Dynasty."