Sandstone is a clastic sedimentary rock composed mainly of sand-sized silicate grains. Sandstones comprise about 20–25% of all sedimentary rocks.
Cut slab of sandstone
Alcove in the Navajo Sandstone
Kokh-type tombs cut into the multicoloured sandstone of Petra
Sand grains of quartz with hematite coating providing an orange colour
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.
A thin section of a clast (sand grain), derived from a basalt scoria. Vesicles (air bubbles) can be seen throughout the clast. Plane light above, cross-polarized light below. Scale box is 0.25 mm.
Claystone from Montana
Conglomerate
Breccia. Notice the angular nature of the large clasts