Rock salt is also called rock salt, and its chemical composition is NaCl. All crystals belong to equiaxed halide. Single crystals are cubes, and stepped depressions often appear on the crystal faces of cubes, and the aggregates are often granular or blocky. Pure stone salt is colorless and transparent. When containing impurities, it is light gray, yellow, red and black, with glass luster. The division of the three cubes is completed. Mohs hardness is 2.5 and specific gravity is 2. 17. Soluble in water. It tastes salty.

Rock salt is a typical chemical sedimentary mineral. In salt lakes or lagoons, it is related to potassium salts and gypsum. Stone salt can be used as food seasoning and preservative, and is an important chemical raw material.

The world-famous producing areas are Salena Basin in the northeast of the United States, Permian Basin in the middle and coastal areas of the Gulf of Mexico, Fergana Valley in Central Asia, Saxony-Angell and other German places. China is rich in rock salt reserves and widely distributed, especially in Qaidam basin, and there are also large-scale rock salt deposits in Sichuan, Hubei, Jiangxi and Jiangsu.

2.NH4HCO3+NaCl=NH4Cl+NaHCO3↓

Sodium bicarbonate precipitates due to its low solubility.

According to the principle that the solubility of NH4Cl is higher than that of NaCl at normal temperature and lower than that of NaCl at low temperature, fine salt powder is added to mother liquor at the temperature of 278 K ~ 283 K (5℃ ~ 10℃) to separate NH4Cl crystals and use it as nitrogen fertilizer alone.