siliciclastics

Siliciclastic rocks are sedimentary rocks composed primarily of silicate minerals that originate from the weathering and erosion of preexisting rocks. They are dominated by silica-rich grains and are distinct from carbonate rocks and siliceous biogenic sediments.

The principal constituents are quartz, feldspar, micas, and various rock fragments, transported as clasts by water, wind, or ice. The major sedimentary rock groups are categorized by grain size: mudstones (clay- and silt-sized material), siltstones, sandstones, and conglomerates or breccias. Within sandstones, textural varieties include quartz arenite (mostly quartz), arkose (significant feldspar), and litharenite (abundant lithic fragments).

Formation occurs in a wide range of environments: rivers and deltas, beaches and dunes, submarine fans, shallow-marine shelves, and lacustrine basins. Transport and sorting influence maturity, with highly mature siliciclastics enriched in quartz and well-sorted grains, whereas immature deposits retain more feldspar and rock fragments.

During diagenesis, grains are compacted and cemented by minerals such as silica, calcite, or iron oxides to form solid rock. Metamorphism can alter siliciclastic rocks into metasandstones or other metamorphic equivalents, but low-grade metamorphism preserves much of the original sedimentary texture.

Siliciclastic rocks are important in geology and industry, serving as major reservoir rocks in petroleum systems and aquifers. Their properties—grain size, sorting, cementation, and mineralogy—record the transport history and paleoenvironments of their source regions.