Greywacke

Pronunciation

• UK IPA: /ˈɡɹeɪwakÉ™/

Alternative forms

• graywacke

Origin

Anglicised form of grauwacke.

Full definition of greywacke

Noun

1. (geology) A hard dark sandstone with poorly sorted angular grains of quartz, feldspar, and small rock fragments in a compact, clay-fine matrix.
• 2004, Richard Fortey, The Earth, Folio Society 2011, p. 177:Endless bleak, rounded hills composed of shales and ribs of tough ‘greywackes’ make up the Southern Uplands – all of such rocks were originally deposited under marine conditions.

Derived terms

• metagreywacke, metagraywacke