klastisch

Klastisch is a geological term used in German- and Dutch-language geology to describe rocks and sediments composed predominantly of fragments (clasts) derived from preexisting rocks. The English equivalent is clastic. The term derives from Greek klastos, meaning "broken."

Klastische sedimentary rocks form by weathering of older rocks, transport of fragments, deposition, and lithification. Clasts vary in size and shape; the classification is chiefly by grain size. Common klastische rocks are: sandstone (sand-sized clasts), siltstone (silt-sized), mudstone or shale (clay- to silt-sized), conglomerate (rounded gravel clasts), and breccia (angular clasts). Matrix and cementing material (quartz, calcite, iron oxides) bind the clasts during diagenesis.

Depositional environments include rivers and streams (fluvial), deltas, beaches, deserts (aeolian), and deep-sea settings (turbidites). The clast composition and sedimentary structures help interpret provenance and transport history. Clastic rocks contrast with chemical rocks formed by precipitation (evaporites, carbonates) or organic rocks such as coal.

Common economic and scientific uses: many reservoir rocks are clastic, like sandstone; lithification processes include compaction and cementation. The study of clastic rocks aids in reconstructing past climates and tectonics.