What Is the Main Source of Salt and How Is It Produced?

November 26, 2025 •

4 min read

Over 250 million metric tonnes of salt are produced globally each year, yet only a small fraction is used for food consumption. So, with such a massive annual demand, what is the main source of salt that supplies our industrial and culinary needs?

Quick Summary

Salt originates from both vast underground rock salt deposits and the world's oceans. It is harvested using several methods, including traditional mining, solar evaporation of seawater or brine, and more advanced vacuum evaporation for higher purity.

Key Points

Rock Salt: Large, underground deposits formed from ancient evaporated seas are a major source of salt, extracted through both traditional cut-and-blast and modern continuous mining techniques.
Solar Evaporation: The sun and wind are used to evaporate seawater or brine in shallow ponds, a method most viable in hot, dry climates.
Vacuum Evaporation: This advanced method involves dissolving underground salt deposits to create pure brine, which is then boiled under a vacuum to produce high-purity salt crystals.
Industrial Use: The vast majority of salt produced globally is for industrial applications, such as de-icing roads and chemical manufacturing, not for human food consumption.
Endless Origin: All salt, whether mined or harvested from modern seas, ultimately has a marine origin, stemming from the evaporation of ancient or contemporary bodies of saltwater.

Earth's Diverse Salt Sources

All salt, or sodium chloride (NaCl), ultimately originates from ancient or modern seas. Millions of years ago, vast oceans and saltwater lakes evaporated, leaving behind thick layers of salt that were subsequently buried under geological formations. These ancient deposits are now mined as rock salt. The world's modern oceans and salt lakes provide a continuously replenishing source, from which salt is extracted through various evaporation techniques. Additionally, concentrated natural brines, which are often groundwater that has dissolved underground salt deposits, serve as a third significant source. The method of extraction depends on the local geology and climate, as well as the purity and end-use of the salt required. Industrial applications, which account for over 90% of global salt usage, typically use less-refined forms, while high-purity applications, such as food and pharmaceuticals, require more intensive processing.

Method 1: Rock Salt Mining

Rock salt, also known as the mineral halite, is the result of ancient evaporated seas. The deposits can be found hundreds or even thousands of feet underground in bedded formations or domelike structures.

There are two primary methods for mining this solid mineral:

Cut and blast mining: This traditional method uses machinery to undercut the base of a solid salt wall. Explosives are then used to blast the salt face, breaking it into large chunks. These chunks are crushed and transported to the surface for further processing. Pillars of salt are intentionally left in place to support the mine's roof, a technique known as "room and pillar" mining.
Continuous mining: This modern technique uses a machine with a rotating head that bores directly into the salt face, grinding the salt into smaller lumps as it goes. This avoids the need for explosives and is often more efficient.

Method 2: Solar Evaporation

This is the oldest and most natural method of salt production, relying on the sun and wind to evaporate water from a brine source. This technique is most efficient in warm climates with low rainfall, such as the Mediterranean and Australia.

Solar evaporation involves a multi-step process:

Concentrating Ponds: Seawater or brine is channeled into a series of shallow, clay-lined ponds. Over time, the sun and wind cause the water to evaporate, gradually increasing the salt concentration.
Crystallizing Ponds: Once the brine reaches a sufficient saturation level, it is moved to crystallizing ponds. Here, the salt precipitates out of the solution and forms a solid crust on the pond's floor.
Harvesting: When the salt layer reaches a certain thickness, it is harvested using mechanical harvesters or, in the case of specialty salts like fleur de sel, by hand. The harvested salt is then washed and dried.

Method 3: Vacuum Evaporation

For applications requiring high-purity salt, especially fine-grained table salt, vacuum evaporation is used. This method is often preceded by solution mining, where fresh water is pumped into underground salt deposits to dissolve the salt and create a pure brine.

Here’s how the process works:

Brine Injection and Retrieval: Wells are drilled into the underground salt formation. Water is injected to dissolve the salt, and the resulting saturated brine is pumped back to the surface.
Purification: The brine is treated to remove impurities, such as calcium and magnesium, before the final evaporation stage.
Evaporation: The purified brine is boiled in a series of large, closed vessels called vacuum pans. Operating under a vacuum allows the water to boil at a lower temperature, which is more energy-efficient. As the water evaporates, very pure salt crystals are formed.
Drying and Packaging: The resulting slurry is centrifuged to remove excess moisture and then dried, sieved, and packaged.

Comparison of Salt Production Methods


Feature	Rock Salt Mining	Solar Evaporation	Vacuum Evaporation
Source	Ancient underground deposits	Seawater, natural brine lakes	Underground deposits (via solution mining)
Process	Blasting and crushing solid rock	Evaporation by sun and wind in ponds	Boiling brine under vacuum
Purity	Often contains mineral impurities (e.g., Himalayan pink salt)	Contains trace minerals from the source water	Highest purity (often >99.9% NaCl)
Energy Use	Mechanical mining equipment, low processing energy	Passive, relies on natural energy	High energy use due to boiling and vacuum
Appearance	Coarse, crystalline chunks; color varies	Variable grain size; can be flaky or coarse	Fine, uniform crystals
Ideal Climate	No climate dependency	Hot, dry climate with low rainfall	No climate dependency

Which Source is Main for What?

While all sources are important, their applications vary. Rock salt is a primary source for de-icing roads in winter due to its abundance and lower cost. A significant portion of mined salt is also used in chemical manufacturing to produce chlorine and caustic soda. Solar evaporation is a major source for culinary and industrial salts in regions with suitable climates. Finally, vacuum evaporation is the go-to method for producing the finest, purest salt for table use, food processing, and pharmaceuticals. Therefore, there isn't a single main source for all salt applications; rather, the primary source depends on the intended end-use and geographical factors.

Conclusion

In summary, the main source of salt is not a single entity but a combination of natural resources and advanced processing. The earth provides ancient rock salt deposits, modern oceans offer a renewable supply for solar evaporation, and natural underground brines yield high-purity salt through vacuum evaporation. Each method, from ancient mining to advanced industrial processes, plays a vital role in meeting the global demand for this essential mineral. The type of salt produced directly reflects its origin and processing, from mineral-rich rock salt to refined, pure table salt.

For a detailed overview of the different salt production techniques, visit the Britannica entry on the subject: Britannica Article on Salt.

Frequently Asked Questions

Yes, all salt, whether it comes from a modern ocean or an underground rock deposit, has a marine origin. The rock salt was formed millions of years ago when ancient seas evaporated, leaving behind salt layers.

The main difference is their origin and refinement level. Rock salt is mined from underground deposits and often contains trace mineral impurities. Sea salt is harvested from evaporating modern seawater and also retains trace minerals. Refined table salt often comes from vacuum-evaporated brine for maximum purity.

Rock salt is mined using methods similar to other minerals. Techniques include 'room and pillar' mining with explosives ('cut and blast') or modern 'continuous mining' where machines bore directly into the salt bed.

While sea salt retains trace minerals that table salt has processed out, the quantities are generally too small to offer significant health benefits. Both are primarily sodium chloride, and moderation is key for health.

The majority of the world's salt (over 90%) is used for industrial purposes. This includes road de-icing, chemical manufacturing (chlorine and caustic soda), and water softening.

Table salt is typically a highly refined product, often made from purified brine through a vacuum evaporation process. This removes most impurities and results in very small, pure crystals. Rock salt is less refined and often contains other minerals.

Solution mining is a modern technique used to extract salt from underground deposits. Water is pumped down into the deposit, dissolving the salt. The resulting concentrated brine is then pumped back to the surface for evaporation.