The mineral commonly known as salt is the ionic compound sodium chloride (NaCl). In its natural, solid state, this compound is called halite, forming transparent or translucent cubic crystals. Halite is abundant across the Earth’s surface and crust, making it a widely distributed geological resource. Sodium chloride is fundamental to life, regulating cellular processes. The primary reservoirs for salt are the world’s oceans, massive underground deposits, and isolated inland water systems.
Salt Found in Seawater and Coastal Areas
The ocean represents the largest single reservoir of sodium chloride in dissolved form. Seawater maintains a consistent salinity, averaging about 35 grams of salt per liter of water (3.5% by weight). This vast supply is the raw material for a significant portion of the world’s salt production, primarily using solar and wind energy.
Salt is obtained from the ocean through solar evaporation in shallow, interconnected pools called salterns. Seawater is progressively concentrated, allowing less soluble salts like calcium carbonate and gypsum to precipitate out first. This controlled, fractional crystallization ensures that sodium chloride begins to crystallize as a purer product when the brine reaches a high concentration.
This natural evaporation process is only viable in regions with high solar insolation and low annual rainfall, such as the Mediterranean and coastal deserts. The resulting salt crystals are then harvested from the floor of the final crystallization ponds. This centuries-old technique remains an efficient way to produce high-purity salt.
Salt Found in Solid Underground Deposits
Vast quantities of salt exist as solid, stratified rock formations deep beneath the Earth’s surface, known as rock salt. These deposits formed millions of years ago when ancient, shallow seas evaporated under arid conditions, leaving behind thick layers of crystallized halite. Over time, these layers were buried by sediments and subjected to tectonic pressure.
In some areas, pressure and heat caused these buried layers to flow upward, piercing the overlying rock to form vertical, cylindrical structures known as salt domes. These features are a major source of halite and are often associated with trapping oil and natural gas deposits. The recovery of this rock salt occurs through two distinct industrial methods: conventional mining and solution mining.
Conventional Mining
Conventional deep-shaft mining involves sinking shafts down to the salt bed. Miners use the “room and pillar” technique, excavating tunnels while leaving large columns of salt in place to support the ceiling.
Solution Mining
Solution mining involves drilling wells into the deposit and injecting water under pressure to dissolve the halite. The resulting saturated saltwater, or brine, is pumped to the surface and evaporated at a plant to recover the purified salt crystals.
Salt Found in Inland Water Bodies
Highly concentrated salt is found in various inland water bodies geographically isolated from the sea. These saline lakes and subsurface brines often have salt concentrations that far exceed those of normal seawater. Their existence is primarily due to endorheic, or closed, drainage basins.
These basins lack an outflow to the sea, meaning water entering the lake can only escape through evaporation. As the water evaporates, it leaves behind all dissolved minerals carried by the inflow, a process called evapoconcentration. This continuous cycle results in the accumulation of extremely high salt levels, creating hypersaline environments.
Examples include the Great Salt Lake and the Dead Sea, which are among the most saline bodies of water on Earth. The chemical composition of these inland brines is highly variable compared to the ocean, often containing high concentrations of other minerals alongside sodium chloride. Salt is also sourced from inland subsurface brines, pumped from underground wells and evaporated on the surface.