Clastic rock

A thin section of a clast (sand grain), derived from a basalt scoria. Vesicles (air bubbles) can be seen throughout the clast. Plane-polarized light above, cross-polarized light below. Scale box is 0.25 mm.

Clastic rocks are composed of fragments, or clasts, of pre-existing minerals and rock. A clast is a fragment of geological detritus, chunks, and smaller grains of rock broken off other rocks by physical weathering. Geologists use the term clastic to refer to sedimentary rocks and particles in sediment transport, whether in suspension or as bed load, and in sediment deposits.

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