Salt is a mineral substance composed primarily of sodium chloride (NaCl), a chemical compound belonging to the larger class of ionic salts, salt in its natural form as a crystalline mineral is known as rock salt or halite. Salt is produced from salt mines or by the evaporation of seawater or mineral-rich spring water in shallow pools. Its major industrial products are caustic soda and chlorine, and it is used in many industrial processes and in the manufacture of polyvinyl chloride, plastics, paper pulp and many other products.