Translations of Encyclopedia about Geology

Salt is a vitally important basic component of our nutrition. We have to replace with food the daily loss of salt which is in our bodies and which we lose by perspiration.

In the ancient world, salt was obtained by boiling and gradual evaporation of seawater. During Middle Ages, when the population had grown considerably and there was a great demand for salt, because it was used heavily to preserve food (salting), the salt was so valuable, that an entire administration was created to regulate its manufacture and commerce. Very often, salt customs fees were an important source of income.

Salts are materials separated from the seawater or the water of inland lakes. In order to obtain salt from seawater, certain conditions must be met. Water must be allowed to evaporate to such a degree so as to liberate the salt. It is possible only if this process takes places at sufficiently high temperatures. In addition, the water must be flowing into a more or less closed pan at a rate lower than the rate of evaporation. If these conditions are present, the first materials to settle are those that do not dissolve easily, such as carbonates (for example, calcite) and sulphates (for example, gypsum), then rock salt (halite), and finally easily soluble minerals such as magnesium chloride and potassium chloride. When unsaturated seawater enters, the process stops.

As a result of the earth's crust movements, it is a frequent occurrence that several layers from different sedimentation processes accumulated one on top of each other. The pressure of the moving earth's crust sometimes pushes salt further down, where under higher temperatures of the earth's interior some salt will change into new salt minerals. This process is called "geothermic metamorphosis."

In contrast, lighter salts ascend due to gravitational movement and folding to the upper regions of the earth's crust. However, it requires a great thickness of the salt deposit, up to several hundred metres, and much thicker mountain range that covers these deposits. Salts travel from their kettles to basins, and these movement produce salt pillows, columns, or walls.

Due to difference of deformation of various salt minerals, there are faults and folds. This process is called "salt tectonics." When in contact with underground water, salt deposits are separated differently. This may be seen on the earth's surface, in the lowering of the salt lakes. In certain places, there are also salt springs which passed to the surface.

Important salt deposits are found in Poland, in the Caspian Sea, and in northern Germany. They formed either during the Devonian or Permian (Cenozoic). In addition to halite and potassium chloride, gypsum and anhydride (formed from gypsum as a result of the pressure of the mountain ranges) are also exploited. They are important for construction and chemical fertilizer industry.

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