feldspathic graywacke

feldspathic graywacke

[fel′spath·ik ′grā‚wak·ə]
(petrology)
Sandstone containing less than 75% quartz and chert and 15-75% detrital clay matrix, and having feldspar grains in greater abundance than rock fragments. Also known as arkosic wacke; high-rank graywacke.