The Economic Aspect of Geology Part 29

Ground barite is also used in certain kinds of rubber goods and in the making of heavy glazed paper. Lesser amounts go into the manufacture of barium chemicals, which are used in the preparation of hydrogen peroxide, in softening water, in tanning leather, and in a wide variety of other applications.

Germany is the world's princ.i.p.al producer of barite and has large reserves of high grade. Great Britain also has extensive deposits and produces perhaps one-fourth as much as Germany. France, Italy, Belgium, Austria-Hungary, and Spain produce smaller but significant amounts.

Before the war the United States imported from Germany nearly half the barite consumed in this country, and produced the remainder. Under the necessities of war times, adequate domestic supplies were developed and took care of nearly all the greatly increased demands. Production has come from fourteen states, the large producers being Georgia, Missouri, and Tennessee. During the war, also, an important movement of barite-consuming industries to the middle west took place, in order to utilize more readily and cheaply the domestic product. For this reason it is not expected that German barite will play as important a part as formerly in American markets,--although it can undoubtedly be put down on the Atlantic seaboard much more cheaply than domestic barite, which requires long rail hauls from southern and middle-western states.

GEOLOGIC FEATURES

The mineral barite is a heavy white sulphate of barium, frequently called "barytes" or "heavy spar." Witherite, the barium carbonate, is a much rarer mineral but is found with barite in some veins.

All igneous rocks contain at least a trace of barium, which is probably present in the silicates, and these small quant.i.ties are the ultimate source of the more concentrated deposits. Barite itself is not found as an original const.i.tuent of igneous rocks or pegmat.i.tes, but is apparently always formed by deposition from aqueous solutions. It is a common gangue mineral in many deposits of metallic sulphides, both those formed in relation to igneous activity and those which are independent of such activity, but in these occurrences it is of little or no commercial importance.

The princ.i.p.al deposits of barite are found in sedimentary rocks, and especially in limestones and dolomites. In these rocks it occurs in veins and lenses very similar in nature to the lead and zinc deposits of the Mississippi valley (p. 211 _et seq._), and, like them, probably deposited by cold solutions which gathered together small quant.i.ties of material from the overlying or surrounding rocks. The Missouri deposits are found in limestones in a region not far from the great southeastern Missouri lead district, and vary from the lead deposits in relative proportions rather than in kind of minerals; the veins consist chiefly of barite, with minor quant.i.ties of silica, iron sulphide, galena, and sphalerite. The deposits of the southern Appalachians occur as lenses in limestones and schists.

Barite is little affected by surface weathering, and tends to remain behind while the more soluble minerals of the a.s.sociated rock are dissolved out and carried away. A limited amount of solution and redeposition of the barite takes place, however, resulting in its segregation into nodules in the residual clays. Most of the barite actually mined comes from these residual deposits, which owe their present positions and values to katamorphic processes. The accompanying clay and iron oxide are removed by washing and mechanical concentration.

Certain investigators of the deposits of the Mississippi valley are extremely reluctant to accept the idea that the ores are formed by surface waters of ordinary temperatures, and are inclined to appeal to heated waters from a hypothetical underlying magmatic source. The fact that barite is a characteristic mineral of many igneous veins, and the fact that in this same general region it is found in the Kentucky-Illinois fluorspar deposits,--where a magmatic source is generally accepted,--together with doubts as to the theoretical efficacy of meteoric waters to transport the minerals found in the barite deposits, have led certain writers to ascribe to these barite deposits a magmatic origin. The magmatic theory has not been disproved; but on the whole the balance of evidence seems strongly to indicate that the barite deposits as well as the lead and zinc ores, which are essentially the same in nature though differing in mineral proportions, have been concentrated from the adjacent sediments by ordinary surface waters.

BORAX

ECONOMIC FEATURES

Borax-bearing minerals are used almost entirely in the manufacture of borax and boric acid. Fully a third of the borax consumed in the United States is used in the manufacture of enamels or porcelain-like coatings for such objects as bathtubs, kitchen sinks, and cooking utensils. Other uses of borax or of boric acid are as a flux in the melting and purification of the precious metals, in decomposing chromite, in making gla.s.s, as a preservative, as an antiseptic, and as a cleansing agent.

Recent developments indicate that the metal, boron, may play an important part in the metallurgy of various metals. It has been used in making very pure copper castings for electrical purposes, in aluminum bronzes, and in hardening aluminum castings; and an alloy, ferroboron, has been shown experimentally to act on steel somewhat like ferrovanadium.

The bulk of the world's borax comes from the Western Hemisphere, the United States and Chile being the two princ.i.p.al producers. There are additional large deposits in northern Argentina, southern Peru, and southern Bolivia, which have thus far been little drawn on because of their inaccessibility. English financial interests control most of these South American deposits.

The only large European producer of borax is Turkey. Italy and Germany produce small amounts. There has also been small production of borax in Thibet, brought out from the mountains on sheep-back.

The United States supplies of borax are sufficient for all domestic requirements and probably for export. Small quant.i.ties of boric acid are imported, but no borax in recent years. The domestic production comes entirely from California, though in the past deposits in Nevada and Oregon have also been worked.

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 princ.i.p.al 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, princ.i.p.ally 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 quant.i.ties 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 a.s.sociated 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 cla.s.s 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 const.i.tute the princ.i.p.al source of domestic borax are not the playa deposits just described, but are ma.s.ses of colemanite in Tertiary clays and limestones with interbedded basaltic flows. The princ.i.p.al 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 a.s.sociated 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 quant.i.ties in sea water. When such water evaporates, it becomes concentrated, along with the magnesium and pota.s.sium salts, in the "mother liquor"; and upon complete evaporation, it crystallizes out as boracite and other rarer minerals. Thus the Sta.s.sfurt 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 pota.s.sium bromide, used in medicine to depress the nervous system.

During the war, large quant.i.ties of bromine were used in asphyxiating and lachrymating gases.

The chief center of the bromine industry in Europe prior to 1914 was Sta.s.sfurt, Germany. No other important commercial source in foreign countries is known, though small quant.i.ties 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 pota.s.sium and sodium bromides and other salts. During the war considerable quant.i.ties 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 quant.i.ties. 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 Sta.s.sfurt salt deposits (p. 113), the bromine salts are crystallized out in the final stages along with the salts of sodium, magnesium, and pota.s.sium. The larger part of the world's bromine has come from the mother liquor resulting from the solution and fractional evaporation of these Sta.s.sfurt 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 subst.i.tute for talc.u.m powder.

Fuller's earths are in general rather widely distributed. The princ.i.p.al 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.

GEOLOGIC FEATURES

Fuller's earth is essentially a variety of clay having a high absorptive power which makes it useful for decolorizing and purifying purposes.

Fuller's earths are in general higher in water content and have less plasticity than most clays, but they vary widely in physical and chemical properties. Chemical a.n.a.lyses are of little value in determining whether a given clay will serve as fuller's earth, and an actual test is the only trustworthy criterion.

Deposits of fuller's earth may occur under the same variety of conditions as deposits of other clays. The deposits of Florida and Georgia consist of beds in slightly consolidated flat-lying Tertiary sediments, which are worked by open cuts. The Arkansas deposits are residual clays derived from the weathering of basic igneous rocks, and are worked through shafts.

GRAPHITE (PLUMBAGO)

ECONOMIC FEATURES

_Crystalline graphite_ is used princ.i.p.ally in the manufacture of crucibles for the melting of bra.s.s, bronze, crucible steel, and aluminum. About 45 per cent of the quant.i.ty and 70 per cent of the value of all the graphite consumed in the United States is employed in this manner. Both _crystalline_ and _amorphous graphite_ are used in lubricants, pencils, foundry facings, boiler mixtures, stove-polishes and paint, electrodes, and fillers or adulterants for fertilizers. The most important use of amorphous graphite is for foundry facings, this application accounting for about 25 per cent of the total United States consumption of graphite of all kinds. _Artificial graphite_ is not suitable for crucibles or pencils but is adapted to meet other uses to which natural graphite is put. It is particularly adapted to the manufacture of electrodes.