sandstones

Sandstone is a clastic sedimentary rock composed mainly of sand-sized grains. Most grains are quartz or feldspar, and the spaces between them are typically filled with a cementing material such as silica, calcite, or iron oxides. The grain size generally ranges from 0.0625 to 2 millimeters, and sandstones are often well sorted and moderately well rounded, though poorly sorted or angular variants occur.

Classification is based on mineral content and texture. Quartz sandstone is dominated by quartz; arkose contains a significant feldspar fraction, usually indicating relatively fresh or nearby source rocks; lithic sandstone includes notable quantities of rock fragments. Greywacke is a poorly sorted sandstone with substantial matrix material and a mix of rock fragments.

Formation and diagenesis occur as sand deposits are buried and lithified. Environments include rivers, deserts, beaches, and continental shelves. After burial, compaction reduces porosity, and cementation binds grains together, producing a durable rock. The cement type and mineralogy influence color, hardness, and weathering behavior.

Uses and properties vary with composition. Sandstones commonly exhibit good porosity and permeability, making them important aquifers and reservoir rocks in oil and gas geology. They are also used as building and decorative stones. Colors range from white to red, yellow, brown, or gray, often reflecting iron oxide content and organic material.

Metamorphically, sandstone can transform into quartzite under high-grade conditions. Sandstones occur worldwide and record a wide range of depositional environments, contributing to regional stratigraphy and landscape formation.