greɪˈwæk

Definitions

1. noun

A type of coarse-grained sandstone or arkose, typically of Precambrian age, that is rich in quartz and feldspar.

“The geologist collected a sample of graywacke from the ancient riverbed.”

2. noun

A type of sedimentary rock that is intermediate in composition and texture between shale and sandstone.

“The geology textbook described the different types of graywacke found in the region.”