Geologic Features
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.
The United States is independent of foreign sources for bromine. The entire domestic tonnage is produced from brines pumped in Michigan, Ohio, West Virginia, and Pennsylvania. A large part of the output is not actually marketed as bromine, but in the form of potassium and sodium bromides and other salts. During the war considerable quantities of bromine materials were exported to Great Britain, France, and Italy.
Geologic Features
Bromine is very similar chemically to chlorine, and is found under much the same conditions, though usually in smaller quantities. The natural silver bromide (bromyrite) and the combined silver chloride and bromide (embolite) are fairly common in the oxide zones of silver ores, but are not commercial sources of bromine.
Bromine occurs in sea water in appreciable amounts, as well as in some spring waters and many natural brines. When natural salt waters evaporate, bromine is one of the last materials to be precipitated, and the residual "mother liquors" or bitterns frequently show a considerable concentration of the bromine. Where complete evaporation takes place, as in the case of the Stassfurt salt deposits (p. 113), the bromine salts are crystallized out in the final stages along with the salts of sodium, magnesium, and potassium. The larger part of the world's bromine has come from the mother liquor resulting from the solution and fractional evaporation of these Stassfurt salts.
The bromine obtained from salt deposits in the eastern United States is doubtless of a similar origin. It is produced as a by-product of the salt industry, the natural or artificial brines being pumped from the rocks (p. 295), and the bromides being extracted either from the mother liquors or directly from the unconcentrated brines.
FULLER'S EARTH
Economic Features
Fuller's earth is used chiefly for bleaching, clarifying, or filtering mineral and vegetable oils, fats, and greases. The petroleum industry is the largest consumer. Minor uses are in the manufacture of pigments for printing wall papers, in detecting coloring matters in certain food-products, and as a substitute for talcum powder.
Fuller's earths are in general rather widely distributed. The principal producers are the United States, England, and the other large consuming countries of Europe. The only important international trade in this commodity consists of exports from the United States to various countries for treating mineral oils, and exports from England for treating vegetable oils.
There is a large surplus production in the United States of fuller's earth of a grade suitable for refining mineral oils, but an inadequate production of material for use in refining edible oils, at least by methods and equipment now in most general use. However, the imports needed from England are more than offset by our exports to Europe of domestic earth particularly adapted to the petroleum industry. Production in the United States comes almost entirely from the southern states; Florida produces over three-fourths of the total and other considerable producers are Texas, Georgia, California, and Arkansas. Imports from England are normally equivalent to about a third of the domestic production.