Yes, salt is mined from underground deposits all over the world, and it has been for centuries. In fact, mining is one of three main ways salt is produced commercially. The others are pumping water into underground salt beds to dissolve it (called solution mining) and evaporating seawater in open ponds. Each method produces salt suited to different purposes, from road deicing to the shaker on your kitchen table.
How Salt Ended Up Underground
The massive salt deposits buried beneath places like Kansas, Texas, and parts of Europe formed over hundreds of millions of years. Ancient seas and shallow lakes evaporated in hot climates, leaving behind layers of salt crystals that were eventually buried under sediment and rock. The U.S. Geological Survey has studied formations in West Texas where salt-bearing layers reach a combined thickness of 1,200 meters. Some of the oldest known rock salt deposits date to the Cambrian period, roughly 500 million years ago.
These deposits are essentially fossil seawater. As shallow bodies of water lost moisture to the sun and wind, the dissolved minerals concentrated until salt crystallized out of solution. Over geologic time, new layers of sediment sealed the salt underground, where it sits today as solid rock waiting to be extracted.
Room and Pillar: Traditional Underground Mining
The most straightforward method is cutting salt directly from underground deposits, much like mining coal or any other mineral. In Kansas, underground salt mines operate at depths between 500 and 1,000 feet. A vertical shaft is drilled through the overlying rock to reach the salt bed, and from there, miners carve out the salt using a technique called room-and-pillar mining.
The process works in a checkerboard pattern. Miners blast or cut large square caverns into the salt, leaving equally large square pillars of salt standing between them to support the rock ceiling above. The blasted salt is crushed into manageable pieces and hauled to the surface through the shaft in large buckets. What’s left behind is a grid of enormous underground rooms separated by thick salt columns, some stable enough to last indefinitely. A few former salt mines have been converted into storage facilities and even tourist attractions.
Salt produced this way comes out as chunky, unrefined rock salt. It contains trace minerals and sediment from the surrounding geology, which gives it a grayish or brownish color. This is the type of salt commonly spread on icy roads in winter.
Solution Mining: Dissolving Salt in Place
Not all mined salt is pulled out as solid rock. In solution mining, freshwater is pumped down a cased well into a buried salt deposit. The water dissolves the salt and forms a concentrated brine, which is then pumped back to the surface. As long as fresh water keeps flowing in and saturated brine keeps coming out, the underground cavern grows larger over time.
Once the brine reaches the surface, it’s evaporated in a series of large sealed vessels called vacuum pans. The result is an extremely pure product: over 99.8% sodium chloride. This high-purity salt is what ends up as table salt, food processing salt, animal feed salt, and water softening salt. Solution mining has been used in central Kansas since before conventional underground mines were established in the region, and it continues today.
Solar Evaporation: The Oldest Method
Before anyone drilled a mine shaft, people were harvesting salt by letting the sun do the work. Solar evaporation dates back to at least 3000 BCE in Mesopotamia, where shallow clay-lined trenches collected seawater and left it to dry. Archaeological evidence from the Persian Gulf region shows that Neolithic communities built salt pans less than 10 centimeters deep, taking advantage of temperature swings between day and night to speed up evaporation. By 2500 BCE, Egyptians were producing salt not only for food but for mummification and trade.
The basic principle hasn’t changed much. Seawater or salty lake water flows into a series of shallow ponds, and sun and wind gradually evaporate the water until salt crystals form on the pond floor. Workers then scrape up the crystals and process them. The method works best in warm, dry, windy climates where solar energy is strong, typically receiving 4 to 8 kilowatt-hours of radiation per square meter each day. Medieval Europe turned solar salt production into a state-controlled industry, with the Venetian Lagoon and France’s Guérande marshes operating vast networks of salt pans. Venetian producers used tidal gates to flush their ponds twice daily, a technique later adopted by Spanish and Portuguese colonies in the Atlantic and Caribbean.
Where All That Salt Actually Goes
Most salt doesn’t end up on food. According to U.S. Geological Survey data, highway deicing accounts for about 42% of all salt consumed in the United States. The chemical industry uses another 39%, with 90% of that arriving as brine rather than solid crystals. Salt is a key raw material for producing chlorine, caustic soda, and a range of industrial chemicals.
The remaining uses break down into smaller slices: distributors handle about 9%, food processing takes 4%, agricultural uses account for 2%, and general industrial applications and water treatment each claim about 1%. The salt you sprinkle on dinner represents a tiny fraction of total production.
From Mine to Table: How Salt Gets Refined
Rock salt pulled from an underground mine and the fine white crystals in a salt shaker are both sodium chloride, but they go through very different levels of processing. Mined rock salt is coarse, contains natural impurities, and is perfectly adequate for deicing roads or feeding into chemical plants. Table salt, whether produced through solution mining or further refinement of mined salt, is processed to remove trace minerals and contaminants, then ground to a uniform grain size.
Most table salt also carries added iodine, a micronutrient included to prevent iodine deficiency disorders. The European Union regulates contaminant levels in food-grade salt, setting maximum limits for mercury at 0.10 milligrams per kilogram and lead at 1.0 milligrams per kilogram for refined salts. Unrefined specialty salts like French grey salt or “fleur de sel” are allowed slightly higher lead levels (2.0 milligrams per kilogram) because they retain more of their natural mineral content.
So-called gourmet salts, including pink Himalayan salt and black Hawaiian salt, get their distinctive colors from those trace minerals. They’re harvested from specific geological deposits or traditional salt pans and undergo minimal processing. The sodium chloride content is slightly lower than refined table salt, but the practical difference in a normal diet is negligible.