Rock salt is also known as 'halite'. The chemical formula for rock salt is NaCl. Rock salt is formed by the evaporation of salty water e.g. sea water. Rock salt deposits can be found in enclosed bays, dry lake beds, inland marginal seas and estuaries in dry regions.
Large bodies of water have also evaporated in the geologic past, and created large amounts of rock salt. These bodies of water include an old ocean that was once in the place of the Atlantic Ocean, and the Mediterranean Sea. The rock deposits were buried by marine sediments, but the density of the halite is less than that of the materials which make up the sediments, and so the salt beds managed to break through the sediments to create domes.
A large amount of rock salt (commercially mined) is prepared for humans to eat. It may also be used to prevent roads from freezing.