Definition of clast in English:

clast

Pronunciation /klast/ /klæst/

noun

Geology
  • A constituent fragment of a clastic rock.

    ‘The clasts in volcaniclastic rocks may range from fine ash to bombs and enormous blocks.’
    • ‘This is substantiated by the presence of eroded Permian carbonate clasts.’
    • ‘The siltstones contain poorly sorted angular fragments of quartz, and angular clasts and cleavage fragments of plagioclase and alkali feldspar.’
    • ‘Geochemical analyses of these clasts show that the eruption tapped two chemically distinct rhyolitic magmas.’
    • ‘The conglomerates contain a mixture of basement-derived clasts and large Upper Permian limestone clasts.’

Origin

1930s back-formation from clastic.