different between graywacke vs greywacke

English

graywacke (countable and uncountable, plural graywackes)

Anglicised form of grauwacke.

greywacke (countable and uncountable, plural greywackes)

(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.

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