Deposits of rock salt are widely distributed in the USA and occur in 25 of the 50 states. Some of the salt deposits are extensive, such as the Salina Group salts of the Michigan and Appalachian Basins, the Permian salts of the Permian Basin, and the Louann salt and salt domes of the Gulf Coast Basin. These occurrences rank among the greatest salt deposits of the world. Most salt deposits in the USA are within major sedimentary basins that received thick accumulations of sediment during periodic marine inundations of parts of the continent in the geological past. They cover a wide span of geological time and range from Silurian to Tertiary. Geological conditions favouring deposition of thick layers of salt were repeated many times in various sedimentary basins. Other salt resources include natural salt brines, salt springs, seawater, and recent surface deposits of salt. Salt and salt brine are currently produced in 15 states, and the United States' estimated 1998 production of 41 Mt of NaCl represents about 22% of the total world production of 186 Mt. In 1998, 31 companies operated 69 salt-producing plants in the United States: 16 plants produced solar-evaporated sa 18 plants, vacuum-pan sa 14 plants, rock sa and 27 plants produced salt brine (several plants produced more than one type of salt). The reported end use of salt during 1998 was for chemicals (50%), ice control (21 %), distributors (various sales and uses) (10%), general industrial (7%), agricultural (4%), food (4%), primary water treatment (1%), and other uses combined with exports (3%).
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