The element boron is present in various complex boro-silicates, such as datolite and tourmaline, the latter of which is used as a precious stone (pp. 290, 293). None of these are commercial sources of borax. The principal boron minerals are borax or "tincal" (hydrated sodium borate), colemanite (hydrated calcium borate), ulexite (hydrated calcium-sodium borate), and boracite (magnesium chloro-borate). Commercially the term borax is sometimes applied to all these materials. These minerals appear in nature under rather widely differing modes of origin.
The borax production of Italy is obtained from the famous "soffioni" or "fumaroles" of Tuscany. These are volcanic exhalations, in which jets of steam carrying boric acid and various borates, together with ammonium compounds, emerge from vents in the ground. The boric acid material is recovered by a process of condensation.
Borates, principally in the form of borax, occur in hot springs and in lakes of volcanic regions. The Thibet deposits, and those formerly worked at Borax Lake, California, are of this type. Certain of the hot-spring waters of the California coast ranges and of Nevada carry considerable quantities of boron, together with ammoniacal salts, and in some places they deposit borax along with sulphur and cinnabar. It seems probable (see p. 40) that these waters may come from an igneous source not far beneath.
Most of the borax deposits of California, Nevada, and Oregon, though not at present the largely producing ones, and probably most of the Chilean and adjacent South American deposits, are formed by the evaporation of desert lakes. They are products of desiccation, and in Chile are associated with the great nitrate deposits (pp. 102-104), which are of similar origin. The salts contained in these deposits are mainly borax, ulexite, and colemanite. The sources of these materials are perhaps deposits of the type mentioned in the last paragraph, or, in California, certain Tertiary borate deposits described below. Whatever their source, the borates are carried in solution by the waters of occasional rains to shallow basins, which become covered with temporary thin sheets of water or "playa lakes." Evaporation of these lakes leaves broad flats covered with the white salts. These may subsequently be covered with drifting sands and capillary action may cause the borates to work up through the sands, becoming mixed with them and efflorescing at the surface. One of the largest of the California deposits of this general class is that at Searles Lake, from which it has been proposed to recover borax along with the potash (pp. 113-114).
The deposits which at present constitute the principal source of domestic borax are not the playa deposits just described, but are masses of colemanite in Tertiary clays and limestones with interbedded basaltic flows. The principal deposits are in Death Valley and adjacent parts of California. The colemanite occurs in irregular milky-white layers or nodules, mingled with more or less gypsum. The deposits are believed to be of the replacement type, rather than ones formed contemporaneously with the sediments. Whether they are due to magmatic solutions carrying boric acid from the associated flows, or to surface waters carrying materials leached from other sediments, is not clear. The crude colemanite as mined carries an average of about 25 per cent B_2O_3; it is treated with soda in the manufacture of borax, or with sulphuric acid in making boric acid.
Boron is present in minute quantities in sea water. When such water evaporates, it becomes concentrated, along with the magnesium and potassium salts, in the "mother liquor"; and upon complete evaporation, it crystallizes out as boracite and other rarer minerals. Thus the Stassfurt salts of Germany (p. 113) contain borates of this type in the carnallite zone of the upper part of the deposits. This is the only important case known of borate deposits of marine origin.
BROMINE
Economic Features
Bromine finds a considerable use in chemistry as an oxidizing agent, in separating gold from other metals, and in manufacturing disinfectants, bromine salts, and aniline colors. The best known and most widely used bromine salts are the silver bromide, used in photography, and the potassium bromide, used in medicine to depress the nervous system. During the war, large quantities of bromine were used in asphyxiating and lachrymating gases.
The chief center of the bromine industry in Europe prior to 1914 was Stassfurt, Germany. No other important commercial source in foreign countries is known, though small quantities have been obtained from the mother liquors of Chile saltpeter and from the seaweed, kelp, in various countries. India has been mentioned as a possible large producer in the future.