Salt, also known as table salt, or rock salt, is a mineral that is composed primarily of sodium chloride. Salt is one of the oldest, most ubiquitous food seasonings and salting is an important method of food preservation. The taste of salt (saltiness) is one of the basic human tastes. Chloride and sodium ions, the two major components of salt, are needed by all known living creatures. Salt is involved in regulating the water content (fluid balance) of the body. While people have used canning and artificial refrigeration to preserve food for the last hundred years or so, salt has been the best-known food preservative, especially for meat, for thousands of years.
Refined salt, which is most widely used presently, is mainly sodium chloride. Food grade salt accounts for only a small part of salt production in industrialised countries (3% in Europe) although worldwide, food uses account for 17.5% of salt production.
Rock salt deposits are formed by the evaporation of ancient salt lakes and may be mined conventionally or through the injection of water. Injected water dissolves the salt, and the brine solution can be pumped to the surface where the salt is collected.
After the raw salt is obtained, it is refined to purify it and improve its storage and handling characteristics. Purification usually involves recrystallization. In recrystallization, a brine solution is treated with chemicals that precipitate most impurities (largely magnesium and calcium salts). Multiple stages of evaporation are then used to collect pure sodium chloride crystals, which are kiln-dried.
Table salt is used in cooking, and also made available to diners in salt shakers on the table. It is refined salt, which contains about 97% to 99% sodium chloride. It usually contains substances that make it free-flowing (anticaking agents) such as sodium silicoaluminate or magnesium carbonate. Table salt has a particle density of 2.165 g/cm3, and a bulk density (dry, ASTM D 632 gradation) of about 1.154 g/cm3.