Sandstone

sandstone, a sedimentary rock composed of sand-size particles which are usually quartz. The grains are commonly held together by natural cement formed by chemical precipitation in the pores. Typically this consists of silica, but may be another material such as calcium carbonate, forming a calcareous sandstone. These variations mean that sandstones vary greatly in fertility and drainage. Sandstones occur in the higher alluvial ground of the River Dordogne, just below the Côtes of st-émilion, and in similar settings elsewhere.