Rock salt is the most common mineral in salt deposits. Rock salt is sodium chloride NaCl with a content of nearly 40% of sodium and 60% of chloride, it often contains an admixture of calcium chloride and magnesium. It is mined in underground mines in the form of blocks, stones or lumps. It can be clear, colorless (in pure form) or tinted gray with clay, red with iron brown with resinous substance, and blue with metallic sodium. It is characterized by excellent solubility in water. We can get this salt in two ways. The first is extraction of mining deposits. The second is extraction from sea water. Solid salt is mined mostly with mining method. Mines usually use a chamber method. In order to find a deposit a shaft is dug, next corridors are built and salt is gradually extracted from the so-called chambers which are 20m wide, 20m high and more than 100m long. The mined salt has crystals of various sizes, from the size of dust particles to large grains. The salt is then ground, sieved and cleaned.
Evaporated salt is purified rock salt. It contains at least 99.9% of sodium chloride and is used as a condiment and ingredient in many processed food products. Its nutrition value is deteriorated by lack of minerals found in natural rock salt, but at the same time the taste is improved as it is more salty comparing to rock salt, which can have a bitter aftertaste. Evaporated salt is artificially enriched with iodine. Vacuum salt mining is based on extraction of so-called brine. Pure and edible salt is produced by evaporation and crystallization of brines. Extracted brine is put in reservoirs and then is chemically clarified. The pure salt solution is taken to a vacuum evaporating dish, where it is heated until it reaches the boiling point. The salt is crystallized to fine crystals containing 2-3% of water and is then dried at 200°C. In this way, salt containing 99% NaCl is produced.
Sea salt. The first reference to sea salt production dates back to the beginning of the second millennium. But even in the Iron Age, sea salt was obtained in the following manner: in order to obtain brine people boiled water with clay and sand taken from salt marshes. In the sixteenth century, with the development of maritime trade, the number of salt mines and salt marshes greatly increased. But it was the beginning of the nineteenth century when sea salt production reached its top. However, half a century later, in the era of emerging salt mines, saline lost its position. Sea salt is more valuable than rock salt because it contains only 34% of sodium chloride and is rich in minerals. This salt is obtained by natural evaporation of sea water kept in clarifiers which are exposed to the sun or artificially with the use of special evaporators. For both methods of sea salt production, water must be heated using solar energy or fire. The higher the temperature at which the evaporation process takes place, the softer, purer and whiter salt. Sea salt has a natural content of iodine. However its content, according to the place of extraction, stands only at about 0.5 to 5mg/kg.