History of salt

Salt, NaCl, is an ionic compound made of sodium and chloride ions. It has been important to humans for thousands of years, because all life has evolved to depend on it. Humans, like all life, need dietary salt to survive. Salt's ability to preserve food was a founding contributor to civilization. It helped to eliminate dependence on seasonal availability of food, and made it possible to ship some foods over long distances. However, salt was difficult to obtain, so it was a highly valued trade item, and considered a form of currency by certain peoples. Many salt roads, such as the via Salaria in Italy, had been established by the Bronze age.

All through history, availability of salt has been pivotal to civilization. In Britain, the suffix "-wich" in a placename means it was once a source of salt, as in Sandwich and Norwich. The Natron Valley was a key region that supported the Egyptian Empire to its north, because it supplied it with a kind of salt that came to be called by its name, natron. Today, salt is almost universally accessible, relatively cheap, and often iodized.

Salt comes from two main sources: sea water and the sodium chloride mineral halite (also known as rock salt). Rock salt occurs in vast beds of sedimentary evaporite minerals that result from the drying up of enclosed lakes, playas, and seas. Salt beds may be up to 350 m thick and underlie broad areas. In the United States and Canada extensive underground beds extend from the Appalachian basin of western New York through parts of Ontario and under much of the Michigan basin. Other deposits are in Texas, Ohio, Kansas, New Mexico, Nova Scotia, and Saskatchewan. In the United Kingdom underground beds are found in Cheshire and around Droitwich. Salzburg, Austria, was named "the city of salt" for its mines. High-quality rock salt was cut in medieval Transylvania, Maramureş and Southern Poland (Wieliczka). Tuzla in Bosnia and Herzegovina was named in Hungarian Só (salt) from the twelfth century on and later "place of salt" by Turks.

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