BORAX (from the Arabic word "būraq", which means "saltpetre" * EN: borax; DE: Borax; FR: borax; ES: borax; RU: бура) is the mineral, the crystalline hydrate of the sodium salt of the tetraboric acid, Na2[V4O5(OH)4]•8N2O. Borax crystallizes into the monoclinic crystal system. There are at the base of the structure of the borax the insular [V4O5(OH)4]2- groups of the boron-oxygen radicals. Borax forms the colourless to white, grayish, greenish, translucent, short-prismatic crystals, more often continuous earthy masses, crusts, lenses, and venules, within the clayish rocks. The cleavage is along 2 directions. Borax is brittle. The hardness is 2-2.5. The density is 1715 kilograms per cubic metre. Borax is soluble within water, melts into the transparent glass with dehydration.

Borax is the typical mineral of the evaporites, it forms itself during the evaporation of the salty lakes. It is accompanied by chlorides, sulphates, and nitrates, of sodium and calcium. The large deposits are located within the USA within California (the Borax and Searles lakes, the Death Valley), the small deposits are known within India, China, and Iran. Borax may be found also in the form of the efflorescences on the soil within the arid regions, and within the depositions of the hot water sources.

Borax is one of the main minerals of the boron ores. Borax is used for the obtainment of boron, during soldering, for the preparation of the optical glasses, enamels, glazes, during the tanning of the skins, for the increasing of the hardness and heat resistance of the metallic products, and so on; it is used as the micro-fertilizer within the agriculture, and also within the medicine, within the metallurgical and other branches of the industry.