Where Does Rock Salt Come From?
Salt remains a basic substance in our lives. We sprinkle it upon french fries, throw it on snowy roads, and use it in specialized aquariums. But who makes it, and how?
Made by People or Mother Nature?
This mineral (halite) is formed naturally and in different areas around the world. Some of the largest spots are in Louisiana, Detroit, and Ontario. Others exist in Germany, Poland, and Romania. Formations can range in depth from several feet to over a thousand. The salt flats of Badwater Basin in Death Valley, California stretch across 200 square miles.
The majority of rock salt forms when saltwater from oceans and inland lakes evaporates and is covered with sedimentation over hundreds or thousands of years. Additionally, certain volcanic events have produced deposits after gases cooled and solidified into solid halite. It often rests among other minerals such as gypsum and calcite.
When rock salt is mined, it is often seen in veins, just like coal. It can also appear in domes – roughly circular plugs of up to a mile across. Standard mining procedures use explosives and heavy equipment to extract the halite and transport it for processing.
The room-and-pillar mining method removes salt in a checkerboard design that leaves behind pillars of the mineral to help support the mine ceiling and create rooms of 18 to 100 feet. In contrast, solution mining injects solvent to dissolve and expedite recovery of the mineral; saturated brine solution pumps to the surface so solar evaporation and other techniques isolate it.
Is It Pure?
Most deposits are filled with crystals that contain other minerals and impurities from nearby soil. As a result, mined salt may have a yellow, gray, black, brown, or red appearance. While road salt used for de-icing remains impure, table salt requires further processing. Various techniques involve chemical treatment, washing with highly concentrated salt water, vacuum evaporation, and the use of a “grainer.” This last method relies on steam flowing through pipes immersed in a brine solution to create flakes of salt that sink to the bottom of a pan.
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