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rock salt:see sodium chloridesodium chloride,
NaCl, common salt. Properties
Sodium chloride is readily soluble in water and insoluble or only slightly soluble in most other liquids. It forms small, transparent, colorless to white cubic crystals.
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halite, table salt. (1) The mineral halite, or, in terms of chemical composition, sodium chloride, NaCl (39.34 percent Na and 60.66 percent CI). Rock salt crystallizes in a cubic system. In nature it is ordinarily encountered in granular crystalline aggregates of varying size. In pure form it is colorless and semitransparent, but more often it is found with admixtures of clay, organic matter, and iron oxide, which tint the halite gray, brown, red, or pink. The hardness on the mineralogical scale is 2; the density is 2.173 kg per cu m. Rock salt is easily soluble in water. There is significant absorption of heat when it is dissolved. Halite that is dissolved or melted (at 772°C) is characterized by high electrical conductivity. It possesses antiseptic properties, protecting saturated organic tissues against putrefactive decomposition.
(2) A sedimentary rock composed almost exclusively or predominantly of halite (in pure varieties, 99 percent or more). The impurity, when present, is usually clay or, less often, fine sandy material, which is either finely dispersed through the rock or in the form of intercalations, seams, or galls. In the clay intercalations or along the periphery of the halite grains (occasionally inside) there are carbonates, anhydrite, authigenic quartz, clay minerals, and, less often, potassium minerals.
A considerable amount of the sodium chloride found in nature has been dissolved in the water of the seas and oceans. Most rock salt, like other salts that have been dissolved in water, was formed through exogenic processes in the basins of arid zones with a negative water balance. Rock salt is produced in small quantities through volcanic activity, in solonchaks, and as a weathering product of chlorine-containing minerals. Rock salt occurs in sedimentary rock in the form of thick seams that extend for dozens of sq km. It also forms cores of domelike structures (salt-dome tectonics) and intercalations, galls, pockets, and impregnations. Mineral deposits of rock salt are encountered in deposits of almost all geological periods. The greatest quantity of salt-bearing rock is concentrated in deposits of the Lower Cambrian, the Middle and Upper Devonian, the Permian, and the Myocene.
Recent salt deposits (native salt; Lakes Baskunchak and El’-ton), associated with Permian salt stocks, are of great industrial interest in the USSR. The largest deposits are located in the Byelorussian SSR (Starobin and Davydovka), the Ukrainian SSR (Solotvin, Romny, Slaviansk and Artemovsk), the Urals (Solikamsk and Shumkovo), the Caspian depression and the adjacent Bashkir and Orenburg-Aktiubinsk salt basins, and Middle Asia. Abroad, rock salt is found in Poland, the German Democratic Republic, the Federal Republic of Germany, Switzerland, Italy, Great Britain, the United States, Canada, and India.
Rock salt deposits are worked by the underground method (with the chamber system) and by leaching. The rock salt, which is pumped out of the deposits through pipes as brine, is evaporated in special vacuum devices (vacuum salt). A considerable amount of the salt (native salt) in the USSR is also obtained by evaporation from salt lakes and salt springs. Rock salt is widely used in the national economy. Purified, it is a very important food product and preservative; it is also used in refrigeration. The chemical industry uses rock salt to produce compounds of sodium or chlorine (ammonium chloride, soda ash, gaseous chlorine, hydrochloric acid, ammonium hydroxide, calcium chloride). Rock salt is used in the aniline dye, paint and varnish, wood chemical, nitrogen, textile, pharmaceutical, metallurgical, leather, petroleum, and plastics industries. Large semi-transparent crystals of rock salt are used in optical instruments.
REFERENCESIvanov, A. A., and Iu. F. Levitskii. Geologiia galogennykh otlozhenii (formatsii) SSSR. Moscow, 1960.
Valiashko, M. G. Geokhimicheskie zakonomernosti formirovaniia mestorozhdenii kaliinykh solei. Moscow, 1962.
Ivanov, A. A., and M. L. Voronova. Galogennye formatsii. Moscow, 1972.
A. B. PAVLOVSKII