Rock salt comes from deposits found around dry lake beds, inland marginal seas and enclosed bays and estuaries. It can also be found in salt springs and underground mines.
When inland lakes, rich in salt, evaporate during dry seasons, the water recedes and salt forms on the evaporated shores. This can also occur when tributaries of salt lakes are diverted for human and agricultural use.
Rock salt is also sometimes found in underground deposits in non-arid regions. These deposits, located far beneath the earth's surface, are mined and salt deposits mix with hot water. This mixture dissolves the salt into a brine, a solution of salt in water, which then evaporates, to create salt crystals. Additionally, rock salt is found in salt springs, where saline water comes out of the ground and forms globular masses.
Most commercial rock salt is created from evaporated salt brine, not from original natural crystals.
Manufacturers often create rock salt artificially. This process involves growing crystals from an evaporated and saturated saltwater solution.
Rock salt is found naturally in many regions of the world. Extensive underground beds run under the Appalachian Basin in the USA and Canada. There are also large salt mines and domes in Europe and the Middle East.