Sandstone is a sedimentary rock composed mainly of sand-sized minerals or rock grains. Most sandstone is composed of quartz and/or feldspar because these are the most common minerals in the Earth's crust. Other common components of sandstone include mica, clay minerals, and iron oxide. Sandstone is formed when sand grains are deposited in layers and then cemented together by a mineral such as calcite, silica, or iron oxide.