There are a number of methods used to produce the salt. Morton Salt uses solar evaporation, rock salt mining and vacuum pan evaporation. Solar evaporation is the oldest method of salt production – used since salt crystals were first noticed in trapped pools of seawater. Its use is practical only in warm climates where the evaporation rate exceeds the precipitation rate, either annually or for extended periods, and ideally, where there are steady prevailing winds. Solar salt production is, typically, the capturing of salt water in shallow ponds where the sun evaporates most of the water. The concentrated brine precipitates the salt which is then gathered by mechanical harvesting machines. Any impurities that may be present in the brine are drained off and discarded prior to harvesting.
Morton also uses the second oldest method of producing salt – underground mining. Large machines travel through vast cave-like passageways performing various operations. Salt may appear in veins, as does coal. Veins are the original bedded salt deposits. Salt also may be found in domes, which were formed when Earth pressures forced salt up through cracks from depths as great as 30,000 or 40,000 feet. Domes resemble plugs of almost circular shape which are a few hundred yards to a mile across. Rock salt typically ranges between 95% and 99% NaCl, and mechanically evaporated salt and solar salt normally exceed 99% NaCl. Evaporated salt made with purified brine has the highest purity, in some cases 99.99% NaCl and is more costly than rock or solar salts.