Salt has been a precious commodity to humans for thousands of years. When humans began trading with others in faraway lands, they would often trade for salt to flavor their food. Today, many mining operations continue extracting salt deposits from the earth.
Rock salt (NaCl, also known as halite or sodium chloride) is mined through solution mining or dry mining. In the first method, miners either pump salt from a shallow well or pour water through a pipe deep into a mine shaft, bringing salt to the surface. According to the American Rock Salt company, table salt has usually been gathered through this method. In dry salt mining, miners must go into vast underground cave networks to collect rock salt deposits.
Rock salt mining companies use a variety of methods to break up the rock salt they find. These include drilling, undercutting and blasting, then crushing so miners can bring it to the surface.
The University of Michigan claims that over 71 trillion unmined tons of salt exist in the Detroit area. Plentiful salt deposits also lie throughout the surrounding region. Salt deposits also exist in many other areas of the United Stats, such as western New York, New Mexico and along the Gulf Coast. They also exist in Nova Scotia, France, Pakistan and many other places.
Rock salt deposits form when large bodies of water, such as lakes, inland seas and oceans, dry up. Sediment deposits cover the salt from those bodies of water, eventually burying it deep beneath the surface. In very arid climates, such as Iran, rock salt sometimes exists on the surface of the earth as well, deposited from dried or drying bodies of water.
The United States and China together produce 40 percent of the world's total salt output per year, according to the Salt Institute. American Rock Salt claims to be the largest rock salt mining company in the United States, with the ability to mine up to 18,000 tons each day. Roughly a quarter billion tons of salt are produced worldwide per year.
People spread rock salt on roads, driveways and sidewalks to thaw ice. People often use a mixture of sand and salt to melt ice while providing traction.
Rock salt deposits often point to the presence of oil deposits, since it can trap petroleum in the earth's crust, says Ken Rubin, a professor in the department of geology and geophysics at the University of Hawaii, Honolulu. Scientists looking for oil often try to locate salt domes, large masses of salt that have been pushed upward by shifts in the earth's crust.
Some rock salt is also processed for consumption, and people use rock salt in making homemade ice cream. The salt makes the ice cream colder by causing it to freeze at a lower temperature.
