Sandstone is a type of rock composed mainly of sand that has been "bonded" together by pressure or by minerals. The sand commonly consists of grains of quartz, feldspar, and other minerals. It may also include organic matter or rock fragments. The minerals that cement the grains include quartz, pyrite, or calcite. The colour of sandstone ranges from cream or grey to red, brown, or green, depending on the cements and impurities in the sand. Brownstone, reddish-brown sandstone, was once widely used to build houses. Sandstone was a common building material for larger structures before reinforced concrete came into use in the middle to late 1800's.