What Are the Two Most Important Sources of Salt?

Salt Make-Up

• Salt (NaCl) is composed of one sodium ion and one chloride ion, and contains 40 percent sodium and 60 percent chloride by weight. Salt is manufactured into several forms for multiple uses. Table salt is finely granulated, created from both rock salt and sea salt, and sometimes has iodine added for the prevention of goiter. Kosher salt is coarse salt that frequently has an anti-caking agent added, though it isn't usually iodized. Canning and pickling salt are fine grain salts used for cooking, and are marketed in large boxes of 3 to 4 lbs. Gourmet sea salts are harvested from saltwater and may be refined into a fine or coarse grain. Rock salt is processed into large, chunky granules that are not meant for human consumption, but are added to ice in homemade ice cream makers or dispersed over roadways for de-icing.

Underground Salt

• One source of salt, rock salt, is found in sedimentary rock, in underground domes or beds up to 1,148 feet thick. Rock salt, which accounts for one-third of the world's salt, occurs in large deposits throughout Austria, Germany, Spain and Louisiana, and in its purest form is edible. Most deposits, however, contain iron oxides, clay or sand, and other contaminants, making refining necessary.

Saltwater Salt

• Salt found dissolved in oceans, some lakes and sea water trapped in shallow ponds produces most of the world's salt. When seawater -- also called saltwater or brine -- evaporates from lagoons and shallow ponds, halite and other minerals are allowed to precipitate out as crystals, creating rock surface salt beds from which salt can be harvested by hand.

How Salt Is Produced

• Underground rock salt must be mined like any other rock or mineral by crushing the salt into manageable-sized lumps and carrying them to the surface. If the salt is particularly hard, regular mining methods may become impossible. In this case, solution mining is used. In solution mining, hot water is pumped into the salt bed or dome, dissolving the halite, which is then pumped out of the ground and evaporated to produce the salt; this is called the vacuum evaporation method. Dry salt lake beds, salt water lakes that have evaporated leaving behind a halite crust up to 12 inches thick, can be "mined" using bulldozers or surface scrapers. Solar evaporation uses wind and sunlight to extract salt from shallow pools of seawater known as saltwater evaporation ponds.