clastic definition
Denoting rocks composed of broken pieces of older rocks: a group of clastic sediments such as conglomerates. More example sentences. 1  Mechanical deposition, by water or wind, produces clastic rocks composed of broken fragments, generally of silicate minerals and small pieces of rock: sandstones and conglomerates. In contrast, the Cambrian clastic rocks are characterized by a paucity of these zircons, suggesting a significant difference between Neoproterozoic and Cambrian drainage systems.