JAMES KING-HOLMES / SCIENCE PHOTO LIBRARY JAMES KING-HOLMES / SCIENCE PHOTO LIBRARY
Rock salt. Piece of rock salt mined from the Cheshire salt plain, UK. Rock salt is formed by precipitation during drying of sea water. As such it forms a sediment known as an evaporite. Evaporites are found as part of marine sedimentary rock sequences. This rock salt has a red-yellow colouration due to sand blown from deserts during its formation in the Jurassic era. The deposits of rock salt on the Cheshire Plain are approximately 30 metres thick and have been mined since 1844. This impure rock salt is used to keep roads free of ice in winter, and in water softening. Purified rock salt has culinary and pharmaceutical uses.
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