Table salt crystals. Coloured scanning electron micrograph (SEM) of crystals of table salt (a form of the mineral sodium chloride, NaCl). Table salt is a fine (small-grained) type that is prepared by refining, grinding and recrystallising natural salts. It also has additives, such as iodine and anti-caking agents to improve diet and make the salt grains flow more freely when added to food. Salt is obtained from salt mines or by evaporating sea water. Magnification: x215 when printed 10cm wide.