Bismuth metal is used in alloys, to which it gives low fusibility combined with hardness and sharp definition. Bismuth alloys are employed in automatic fire sprinklers, in safety plugs for boilers, in electric fuses, in solders and dental amalgams, and in some type and bearing metals. Bismuth salts find a considerable application for pharmaceutical purposes, especially in connection with intestinal disorders, and the best grades of bismuth materials are used for this purpose. The salts are also used in porcelain painting and enameling and in staining glass.
Bolivia is the most important producer of bismuth ore. The output is controlled entirely by British smelting interests. An important deposit exists in Peru, the output of which is limited by the same British syndicate. Considerable bismuth is produced in Australia, Tasmania, and New Zealand, all of which likewise goes to England. Germany before the war had three smelters which produced bismuth from native ores in Saxony; bismuth was one of the few metals of which Germany had an adequate domestic supply. Recently southern China is reported to be mining increasing amounts of bismuth.
The United States produces the larger part of its bismuth requirements, chiefly from plants installed at two lead refineries. A further installation would make this country entirely independent of foreign supplies if occasion required. Imports, from England and South America, have been steadily declining, but during the war were somewhat increased. The United States does not export bismuth so far as known.
The principal minerals of bismuth are bismuthinite (bismuth sulphide), bismutite (hydrated carbonate), bismite or bismuth ocher (hydrated oxide), and native bismuth.
The native metal and the sulphide are believed to be formed mainly as primary minerals of igneous origin. In the deposits of New South Wales they are found associated with molybdenite inquartz gangue, in pipe-like deposits in granite. The oxide and the carbonate are probably products of surface weathering. The Bolivian deposits contain the native metal, the oxide, and the carbonate, associated with gold, silver, and tin minerals, in one locality in slates and in another locality in porphyry. The origin is not well known.
In the United States, the sulphide, bismuthinite, is found in the siliceous ores of Goldfield, Nevada (p. 230), and in minor amounts in a great number of the sulphide ores of the Cordilleran region. The ores of the Leadville and Tintic districts (pp. 219 and 235) yield the larger part of the United States production, the bismuth being recovered as by-product from the electrolytic refining of the lead bullion. Large amounts of bismuth pass out of the stacks of smelters treating other western ores, and while it would not be cheap nor easy to save the bismuth thus lost, it could probably be done in case of necessity.
Cadmium is used in low melting-point alloys—as, for example, those employed in automatic fire-extinguishers and electric fuses,—in the manufacture of silverware, and in dental amalgams. During the war the critical scarcity of tin led to experiments in the substitution of cadmium for tin in solders and anti-friction metals. Results of some of these experiments were promising, but the war ceased and demands for tin decreased before the cadmium materials became widely used. Future developments in this direction seem not unlikely. Cadmium compounds are used as pigments, particularly as the sulphide "cadmium yellow," and to give color and luster to glass and porcelain. Cadmium salts are also variously used in the arts, in medicine, and in electroplating.
Practically the entire cadmium output of the world comes from Germany and the United States. In addition, England produces a very small quantity. Before the war Germany produced about two-thirds of the world's total, and supplied the European as well as a considerable part of the United States consumption. During the war the United States production increased three to four fold, imports ceased, and considerable quantities were exported to theallied nations in Europe and to Japan. At present the United States is entirely independent as regards cadmium supplies. Production is sufficient to supply all the home demand and to permit exports of one-third of the total output. A considerable number of possible cadmium sources are not being used, and the production is capable of extension should the need arise.
Nearly the only cadmium mineral known is the sulphide, greenockite, but no deposits of this mineral have been found of sufficient volume to be called cadmium ores. Sphalerite almost always contains a little cadmium, probably as the sulphide; and in zinc deposits crystals of sphalerite in cavities are frequently covered with a greenish-yellow film or coating of greenockite. These coatings have probably been formed by the decomposition of cadmium-bearing zinc sulphide in the oxide zone, the carrying down of the cadmium in solution, and its precipitation as secondary cadmium sulphide. The zinc oxide minerals in the surficial zone also are sometimes colored yellow by small amounts of greenockite. In the zinc ores of the Joplin district of Missouri, cadmium is present in amounts ranging from a trace to 1 per cent and averaging 0.3 per cent.
Germany's cadmium is produced by fractional distillation of the Silesian zinc ores, which contain at most 0.3 per cent cadmium. In the United States there are large potential sources in the zinc ores of the Mississippi valley, and considerable cadmium is recovered in roasting them. Much of the American cadmium is also obtained from bag-house dusts at lead smelters.
The general geologic conditions of the cadmium-bearing ores are indicated in the discussion of lead and zinc deposits in an earlier chapter.
Cobalt finds its largest use in the form of cobalt salts, employed in coloring pottery and glass and in insect poisons. Cobalt is also used in some of the best high-speed tool steels. "Stellite," which is used to a limited extent in non-rusting tools of various sorts,and in considerable quantity to replace high-speed tool steels, is an alloy of cobalt, chromium, and small quantities of other metals. Considerable experimental work has been done on the properties and uses of cobalt alloys, and their consumption is rapidly on the increase.
Cobalt is an item of commerce of insignificant tonnage. There are only two countries, Canada (Ontario) and the Belgian Congo, which produce noteworthy amounts. The Katanga district in the Congo produces blister copper that contains as much as 4 per cent of cobalt, though usually less than 2 per cent. This product formerly went to Germany, and now goes entirely to Great Britain. Just how much cobalt is saved is unknown, but probably several hundred tons annually. It is probable that most of the cobalt in these ores will be lost on the installation of a leaching process for recovery of the copper. Canada exports most of its product to the United States, though the amount is small. Domestic production in this country has been too small to record. The United States has been dependent on imports from Canada.
The principal cobalt minerals are smaltite (cobalt arsenide), cobaltite (cobalt-arsenic sulphide), and linnæite (cobalt-nickel sulphide). Under weathering conditions these minerals oxidize readily to form asbolite, a mixture of cobalt and manganese oxides, and the pink arsenate, erythrite or "cobalt bloom."
Cobalt minerals are found principally in small quantities disseminated through ores of silver, nickel, and copper. The production of Canada is obtained mainly as a by-product of the silver ores of the Cobalt district (described on pp. 234-235), and smaller amounts are recovered from the Sudbury nickel ores (pp. 180-182). The cobalt of Belgian Congo is obtained from rich oxidized copper ores which impregnate folded sediments (p. 205).
Uses of mercury are characterized by their wide variety and their application to very many different phases of modernindustry; they will be named here in general order of decreasing importance. About one-third of the mercury consumed in this country goes into the manufacture of drugs and chemicals, such as corrosive sublimate, calomel, and glacial acetic acid. Mercury fulminate is used as a detonator for high explosives and to some extent for small-arms ammunition—a use which was exceedingly important during the war, but is probably of minor consequence in normal times. Mercuric sulphide forms the brilliant red pigment, vermilion, and mercuric oxide is becoming increasingly important in anti-fouling marine paint for ship-bottoms. Either as the metal or the oxide, mercury is employed in the manufacture of electrical apparatus (batteries, electrolyzers, rectifiers, etc.), and in the making of thermostats, gas governors, automatic sprinklers, and other mechanical appliances. Mercuric nitrate is used in the fabrication of felt hats from rabbits' fur. In the extraction of gold and silver from their ores by amalgamation, large amounts of metallic mercury have been utilized, but of late years the wide application of the cyanide process has decreased this use. Minor uses include the making of certain compounds for preventing boiler-scale, of cosmetics, and of dental amalgam.
The ores of mercury vary greatly in grade. Spanish ores yield an average in the neighborhood of 7 per cent, Italian ores 0.9 per cent, and Austrian ores 0.65 per cent of metallic mercury. In the United States the ores of California yield about 0.4 per cent and those of Texas range from about 0.5 to 4 per cent. In almost all cases the ores are treated in the immediate vicinity of the mines, and fairly pure metal is obtained by a process of sublimation and condensation. This is usually marketed in iron bottles or flasks containing 75 pounds each.
The large producers of mercury are, in order of normal importance, Spain, Italy, Austria, and United States. Mexico, Russia, and all other countries produce somewhat less than 5 per cent of the world's total.
The largest quicksilver mines of the world are those of Almaden in central Spain, which are owned and operated by the Spanish government. This government, after reserving a small amount for domestic use, sells all the balance of the production through the Rothschilds of London. In addition British capital controls some smaller mines in northern Spain. England thus largely controlsthe European commercial situation in this commodity, and London is the world's great quicksilver market, where prices are fixed and whence supplies go to all corners of the globe. Reserves of the Almaden ore bodies are very large. Sufficient ore is reported to have been developed to insure a future production of at least 40,000 metric tons—an amount equivalent to the entire world requirements at pre-war rates of consumption for 100 years.
The mercury deposits of the Monte Amiata district of central Italy were in large part dominated by German capital, but during the war were seized by the Italian government. The mines of Idria, Austria-Hungary, were owned by the Austrian government and their ultimate control is at present uncertain. Reserves are very large, being estimated at about one-half those of Almaden. Although England has had a considerable control over the prices and the market for mercury, the Italian and Austrian deposits have provided a sufficient amount to prevent any absolute monopoly. English interests have now secured control of the Italian production, and it is expected that they will also control the Austrian production—thus giving England control of something over three-fourths of the world's mercury.
In the United States about two-thirds of the mercury is produced in the Coast Range district of California, and most of the remainder in the Terlingua district of Texas. Smaller quantities come from Nevada, Oregon, and a few other states. The output before the war was normally slightly in excess of domestic demand and some mercury was exported to various countries. Due to the exhaustion of the richer and more easily worked deposits, however, production was declining. During the war, with increased demands and higher prices, production was stimulated, the United States became the largest mercury-producing country in the world, and large quantities were exported to help meet the military needs of England and France.
With the end of war prices and with high costs of labor and supplies, production in the United States has again declined. Many of the mines have passed their greatest yield, and though discovery of new ore bodies might revive the industry, production is probably on the down grade. Future needs of this country will probably in some part be met by imports from Spain, Italy, and Austria, where the deposits are richer and labor is cheaper. Thissituation has caused much agitation for a tariff on imports. The present tariff of 10 per cent is not sufficient to keep out foreign mercury.
Outside of the United States large changes in distribution of production of quicksilver are not expected for some time. The reserves of the European producers are all large and are ample to sustain present output for a considerable number of years. It is reported that there will be a resumption of mining in the once very productive Huancavelica District of Peru and in Asia Minor, and with restoration of political order there may be an increase in output from Mexico and Russia,—but these districts will be subordinate factors in the world situation. On geologic grounds, new areas of mercury ores may be looked for in regions of recent volcanic activity, such as the east coast of Asia, some islands of Oceania, the shores of the Mediterranean, and the Cordilleras of North and South America,—but no such areas which are likely to be producers on a large scale are now known.
The chief mineral of mercury, from which probably over 95 per cent of the world's mercury comes, is the brilliant red sulphide, cinnabar. Minor sources include the black or gray sulphide, metacinnabar, the native metal, and the white mercurous chloride, calomel. The ores are commonly associated with more or less iron sulphide, and frequently with the sulphides of antimony and arsenic, in a gangue consisting largely of quartz and carbonates (of calcium, magnesium, and iron). The precious metals and the sulphides of the base metals are rare.
Mercury deposits are in general related to igneous rocks, and have associations which indicate a particular type of igneous activity. They are not found in magmatic segregations, in pegmatites, nor in veins which have been formed at great depths and under very high temperatures. On the contrary, the occurrence of many deposits in recent flows which have not been eroded, their general shallow depth (large numbers extending down only a few hundred feet), and the association of some deposits with active hot springs now carrying mercury in solution, suggest an origin through the work of ascending hot waters near the surface. Themercury minerals are believed to have been carried in alkaline sulphide solutions. Precipitation from such solutions may be effected by oxidation, by dilution, by cooling, or by the presence of organic matter. Being near the surface, it is a natural assumption that the waters doing the work were not intensely hot. At Sulphur Bank Springs, in the California quicksilver belt, deposition of cinnabar by moderately hot waters is actually taking place at present; also these waters are bleaching the rock in a manner often observed about mercury deposits.
The Coast Ranges of California contain a great number of mercury deposits extending over a belt about 400 miles long. The ore bodies are in fissured zones in serpentine and Jurassic sediments, and are related in general to recent volcanic flows. A considerable amount of bituminous matter is found in the ores, and is believed to have been an agent in their precipitation.
The Terlingua ores of Texas are found in similar fractured zones in Cretaceous shales and limestones associated with surface igneous flows. The occurrence of a few ore bodies in vertical shoots in limestone, apparently terminating upward at the base of an impervious shale, furnishes an additional argument for their formation by ascending waters.
In the few deposits (e. g., those of Almaden, Spain, and of the deep mines of New Almaden and New Idria, California,) where there is no such clear relation to volcanic rocks as generally observed, but where the ores contain the same characteristic set of minerals, it is concluded that practically the same processes outlined above have been active in their formation; and that the volcanic source of the hot solutions either failed to reach the surface or has been removed by erosion. The same line of reasoning is carried a step further, and in many gold-quartz veins in volcanic rocks, where cinnabar and its associated minerals are present, it is believed that waters of a hot-spring nature have again been effective. Thus cinnabar, when taken with its customary associations, is regarded as a sort of geologic thermometer.
In the weathering of mercury deposits, cinnabar behaves somewhat like the corresponding silver sulphide, argentite. In the oxide zone, native mercury and the chloride, calomel, are formed. In the Texas deposits a red oxide and a number of oxychlorides are also present. The carrying down of the mercury and itsprecipitation as secondary sulphide may have taken place in some deposits, but this process is unimportant in forming values.
The largest use of tin is in the manufacture of tin-plate, which is employed in containers for food, oil, and other materials. Next in importance is its use in the making of solder and of babbitt or bearing metal. Tin is also a constituent of certain kinds of brass, bronze, and other alloys, such as white metal and type metal. Minor uses include the making of tinfoil, collapsible tubes, wire, rubber, and various chemicals. Tin oxide is used to some extent in white enameling of metal surfaces. Roughly a third of the tin consumed within the United States goes into tin-plate, a third into solder and babbitt metal, and a third into miscellaneous uses.
The ores of tin in general contain only small quantities of the metal. Tin has sufficient value to warrant the working of certain placers containing only a half-pound to the cubic yard, although the usual run is somewhat higher. The tin content of the vein deposits ranges from about 1 per cent to 40 per cent, and the average grade is much closer to the lower figure.
Great Britain has long controlled the world's tin ores, producing about half of the total and controlling additional supplies in other countries. The production is in small part in Cornwall, but largely in several British colonies—the Malay States, central and south Africa, Australia, and others. The Malay States furnish about a third of the world's total. Another third is produced in immediately adjacent districts of the Dutch East Indies, Siam (British control), and China, and some of the concentrates of these countries are handled by British smelters, especially at Singapore.
Tin is easily reduced from its ores and most of the tin is smelted close to the sources of production. Considerable quantities, however, have gone to England for treatment. London has been the chief tin market of the world, and before the war the larger portion of the tin entering international trade went through this port. During the war a good deal of the export tin from Straits Settlements was shipped direct to consumers rather than via London, but it is not certain how future shipments may be made.
Significant features of the tin situation in recent years have been a decline of production in the Malay States, and a large and growing production in Bolivia. Malayan output has decreased because of the exhaustion of some of the richer and more accessible deposits; certain governmental measures have also had a restrictive effect. Bolivian production now amounts to over a fifth of the world's total and bids fair to increase. About half the output is controlled by Chilean, and small amounts by American, French, and German interests. A large portion of the Bolivian concentrates formerly went to Germany for smelting, but during the war American smelters were developed to handle part of this material; large quantities are also smelted in England.
The United States produces a small fraction of 1 per cent of the world's tin, and consumes a third to a half of the total. The production is mainly from the Seward Peninsula of northwestern Alaska. For American tin smelters, Bolivia is about the only available source of supplies; metallic tin can be obtained from British possessions, but no ore, except by paying a 33-⅓ per cent export tax. The United States exports tin-plate in large amounts, and in this trade has met strong competition from English and German tin-plate makers.
A world shortage of tin during the war required a division of available supplies through a central international committee. Somewhat later, with the removal of certain restrictions on the distribution of tin, considerable quantities which had accumulated in the Orient found their way into Europe and precipitated a sensational slump in the tin market.
The principal mineral of tin is cassiterite (tin oxide). Stannite, a sulphide of copper, iron, and tin, is found in some of the Bolivian deposits but is rare elsewhere.
About two-thirds of the world's tin is obtained from placers and one-third from vein or "lode" deposits. Over 90 per cent of the tin of southeastern Asia and Oceania is obtained from placers. Tin placers, like placers of gold, platinum, and tungsten, represent concentrations in stream beds and ocean beaches of heavy, insoluble minerals—in this case chiefly cassiterite—which werepresent in the parent rocks in much smaller quantities, but which have been sorted out by the classifying action of running water.
The original home of cassiterite is in veins closely related to granitic rocks. It is occasionally found in pegmatites, as in certain small deposits of the Southern Appalachians and the Black Hills of South Dakota, or is present in a typical contact-metamorphic silicated zone in limestone, as in some of the deposits of the Seward Peninsula of Alaska. In general, however, it is found in well-defined fissure veins in the outer parts of granitic intrusions and extending out into the surrounding rocks. With the cassiterite are often found minerals of tungsten, molybdenum, and bismuth, as well as sulphides of iron, copper, lead, and zinc, and in some cases there is evidence of a rough zonal arrangement. The deposits of Cornwall and of Saxony show transitions from cassiterite veins close to the intrusions into lead-silver veins at a greater distance. The gangue is usually quartz, containing smaller amounts of a number of less common minerals—including lithium mica, fluorite, topaz, tourmaline, and apatite. The wall rocks are usually strongly altered and in part are replaced by some of the above minerals, forming coarse-grained rocks which are called "greisen."
The origin of cassiterite veins, in view of their universal association with granitic rocks, is evidently related to igneous intrusions. The occurrence of the veins in distinct fissures in the granite and in the surrounding contact-metamorphic zone indicates that the granite had consolidated before their formation, and that they represent a late stage in the cooling. The association with minerals containing fluorine and boron, and the intense alteration of the wall rocks, indicate that the temperature must have been very high. It is probable that the temperature was so high as to cause the solutions to be gaseous rather than liquid, and that what have been called "pneumatolytic" conditions prevailed; but evidence to decide this question is not at present available.
The most important deposits of tin in veins are those of Bolivia, some of which are exceptionally rich. These are found in granitic rocks forming the core of the high Cordillera Real and in the adjacent intruded sediments, in narrow fissure veins and broader brecciated zones containing the typical ore and gangue minerals described above, and also, in many cases, silver-bearing sulphides(chiefly tetrahedrite). There appear to be all gradations in type from silver-free tin ores to tin-free silver ores, although the extremes are now believed to be rare. In the main the tin ores, with abundant tourmaline, appear to be more closely related to the coarse-grained granites, and to indicate intense conditions of heat and pressure, while the more argentiferous ores, with very little or no tourmaline, are found in relation to finer-grained quartz porphyries and even rhyolites, and seem to indicate less intense conditions at the time of deposition. The ores of the whole area, which is a few hundred miles long, have been supposed to represent a single genetic unit, and the sundry variations are believed to be local facies of a general mineralization. Processes of secondary enrichment have in places yielded large quantities of oxidized silver minerals and wood tin near the surface, with accumulations of ruby silver ores at greater depths.
The only other vein deposits which are at present of consequence are those of Cornwall. Here batholiths of granite have been intruded into Paleozoic slates and sandstones, and tin ores occur in fissures and stockworks in the marginal zones. With the exhaustion of the more easily mined placers, the lode deposits will doubtless be of increasing importance.
Cassiterite is practically insoluble and is very resistant to decomposition by weathering. Oxide zones of tin deposits are therefore enriched by removal of the more soluble minerals. Stannite probably alters to "wood tin," a fibrous variety of cassiterite. Secondary enrichment of tin deposits by redeposition of tin minerals is negligible.
Radium salts are used in various medical treatments—especially for cancer, internal tumors, lupus, and birth marks—and in luminous paints. During the latter part of the war it is estimated that over nine-tenths of the radium produced was used in luminous paints for the dials of watches and other instruments. In addition part of the material owned by physicians was devoted to this purpose, and it is probable that the accumulated stocks held by the medical profession were in this way reduced byone-half. The greatly extended use of radium, together with the distinctly limited character of the world's known radium supplies, has led to some concern; and considerable investigation has been made of the possibilities of mesothorium as a substitute for radium in luminous paints. Low-grade radium residues are used to some extent as fertilizers.
Uranium has been used as a steel alloy, but has not as yet gained wide favor. Uranium salts have a limited use as yellow coloring agents in pottery and glass. The principal use of uranium, however, is as a source of radium, with which it is always associated.
European countries first developed the processes of reduction of radium salts from their ores. Most of the European ores are obtained from Austria, where the mines are owned and operated by the Austrian government, and small quantities are mined in Cornwall, England, and in Germany. Production is decreasing. The European hospitals and municipalities have acquired nearly all of the production.
The United States has the largest reserves of radium ore in the world, and the American market has in recent years been supplied from domestic plants. Before the war, radium ores were shipped to Europe for treatment in Germany, France, and England, and radium salts were imported from these countries. There are now radium plants in the United States capable of producing annually from domestic ores an amount several times as large as the entire production of the rest of the world. Practically all the production has come from Colorado and Utah. Known reserves are not believed to be sufficient for more than a comparatively few years' production, but it is not unlikely that additional deposits will be found in the same area.
Uranium is one of the rarer metals. Radium is found only in uranium ores and only in exceedingly small quantities. The maximum amount which can be present in a state of equilibrium is about one part of radium in 3,000,000 parts of uranium. The principal sources of uranium and radium are the minerals carnotite (hydrous potassium-uranium vanadate) and pitchblende or uraninite (uranium oxide).
The deposits of Joachimsthal, Bohemia, contain pitchblende, along with silver, nickel, and cobalt minerals and other metallic sulphides, in veins associated with igneous intrusions.
The important commercial deposits of Colorado and Utah contain carnotite, together with roscoelite (a vanadium mica) and small amounts of chromium, copper, and molybdenum minerals, as impregnations of flat-lying Jurassic sandstones. The ores carry up to 35 per cent uranium oxide (though largely below 2 per cent), and from one-third as much to an equal amount of vanadium oxide. The ore minerals are supposed to have been derived from a thick series of clays and impure sandstones a few hundred feet above, containing uranium and vanadium minerals widely disseminated, and to have been carried downward by surface waters containing sulphates. The ore bodies vary from very small pockets to deposits yielding a thousand tons or so, and are found irregularly throughout certain particular beds without any special relation to present topography or to faults. The association of many of the deposits with fossil wood and other carbonaceous material suggests that organic matter was an agent in their precipitation, but the exact nature of the process is not clear. In a few places in Utah the beds dip at steep angles, and the carnotite appears in spots along the outcrops and generally disappears as the outcrops are followed into the hillsides; this suggests that the carnotite may be locally redissolved and carried to the surface by capillary action, forming rich efflorescences. Because of the nature of the deposits no large amount of ore is developed in advance of actual mining; but estimates based on past experience indicate great potentialities of this region for future production.
In eastern Wyoming is a unique deposit of uranium ore in a quartzite which lies between mica-schist and granite. The principal ore mineral is uranophane, a hydrated calcium-uranium silicate, which is believed to be an oxidation product of pitchblende. Some of the ore runs as high as 4 per cent uranium oxide, and the ore carries appreciable amounts of copper but very little vanadium.
Very recently radium ores have been discovered in the White Signal mining district of New Mexico, which was formerly worked for gold, silver, copper, and lead. The radium-bearing minerals are torbernite and autunite (hydrous copper-uranium andcalcium-uranium phosphates), and are found in dark felsite dikes near their intersections with east-west gold-silver-quartz veins. The possibilities of this district have not yet been determined.
Pitchblende has been found in gold-bearing veins in Gilpin County, eastern Colorado, and in pegmatite dikes in the Appalachians, but these deposits are of no commercial importance. Pitchblende is grayish-black, opaque, and so lacking in distinctive characteristics that it may readily be overlooked; hence future discoveries in various regions would not be surprising.
Natural abrasives are less important commercially in the United States than artificial abrasives, but a considerable industry is based on the natural abrasives.
Silica or quartz in its various crystalline forms constitutes over three-fourths of the tonnage of natural abrasives used in the United States. It is the chief ingredient of sand, sandstone, quartzite, chert, diatomaceous earth, and tripoli. From the sand and sandstone are made millstones, buhrstones, grindstones, pulpstones, hones, oilstones, and whetstones. Sand, sandstone, and quartzite are also ground up and used in sand-blasts, sandpaper, and for other abrasive purposes. Chert or flint constitutes grinding pebbles and tube-mill linings, and is also ground up for abrasives. Diatomaceous (infusorial) earth is used as a polishing agent and also as a filtering medium, an absorbent, and for heat insulation. Tripoli (and rottenstone) are used in polishing powders and scouring soaps as well as for filter blocks and many other purposes.
Other important abrasives are emery and corundum, garnet, pumice, diamond dust and bort, and feldspar.
Imports of abrasive materials into the United States have about one-third of the value of those locally produced. While all of the various abrasives are represented in these imports, the United States is dependent on foreign sources for important parts of its needs only of emery and corundum, garnet, pumice, diamond dust and bort, and grinding pebbles.
Emery and corundum are used in various forms for the grinding and polishing of hard materials—steel, glass, stone, etc. Theprincipal foreign sources of emery have been Turkey (Smyrna) and Greece (Naxos) where reserves are large and production cheap. Production of corundum has come from Canada, South Africa, Madagascar, and India. The domestic production of emery is mainly from New York and Virginia, and corundum comes from North Carolina. Domestic supplies are insufficient to meet requirements, and cannot be substituted for the foreign material for the polishing of fine glass and other special purposes. Curtailment of imports during the war greatly stimulated the development of artificial abrasives and their substitution for emery and corundum.
Garnet is used chiefly in the form of garnet paper for working leather, wood, and brass. Garnet is produced mainly in the United States and Spain. The United States is the only country using large amounts of this mineral and imports most of the Spanish output. The domestic supply comes mainly from New York, New Hampshire, and North Carolina.
Pumice is used in fine finishing and polishing of varnished and enameled surfaces, and in cleaning powders. The world's principal source for pumice is the Lipari Islands, Italy. There is a large domestic supply of somewhat lower-grade material (volcanic ash) in the Great Plains region, and there are high-grade materials in California and Arizona. Under war conditions these supplies were drawn on, but normally the high-quality Italian pumice can be placed in American markets more cheaply.
Diamond dust is used for cutting gem stones and other very hard materials, and borts or carbonadoes (black diamonds) for diamond-drilling in exploration. Most of the black diamonds come from Brazil, and diamond dust comes from South Africa, Brazil, Borneo, and India.
Chert or flint pebbles for tube-mills are supplied mainly from the extensive deposits on the French and Danish coasts. The domestic production has been small, consisting principally of flint pebbles from the California beaches, and artificial pebbles made from rhyolite in Nevada and quartzite in Iowa. War experience demonstrated the possibility of using the domestic supply in larger proportion, but the grade is such that in normal times this supply will not compete with importations.
Feldspar as an abrasive is used mainly in scouring soaps and window-wash. Domestic supplies are ample. The principal useof feldspar is in the ceramic industry and the mineral is discussed at greater length in the chapter on common rocks (p. 86).
For the large number of abrasives produced from silica, outside of flint pebbles, domestic sources of production are ample. Siliceous rocks are available almost everywhere. For particular purposes, however, rocks possessing the exact combinations of qualities which make them most suitable are in many cases distinctly localized.Millstones and buhrstones, used for grinding cereals, paint ores, cement rock, fertilizers, etc., are produced chiefly in New York and Virginia; partly because of trade prejudice and tradition, about a third of the American requirements are imported from France, Belgium, and Germany.Grindstones and pulpstones, used for sharpening tools, grinding wood-pulp, etc., come mainly from Ohio and to a lesser extent from Michigan and West Virginia; about 5 per cent of the consumption is imported from Canada and Great Britain.Hones,oilstones, andwhetstonesare produced largely from a rock called "novaculite" in Arkansas, and also in Indiana, Ohio, and New England; imports are negligible.Flint liningsfor tube-mills were formerly imported from Belgium, but American products, developed during the war in Pennsylvania, Tennessee, and Iowa, appear to be wholly satisfactory substitutes.Diatomaceous earthis produced in California, Nevada, Connecticut, and Maryland, andtripoli and rottenstonein Illinois, Missouri, and Oklahoma; domestic sources are sufficient for all needs, but due to questions of back-haul and cost of rail transportation there has been some importation from England and Germany.
The geologic features of silica (quartz), feldspar, and diamonds are sufficiently indicated elsewhere (Chapter II; pp. 84, 196, 86, 291-292).
Diatomaceous earth is made up of remains of minute aquatic plants. It may be loose and powdery, or coherent like chalk. It is of sedimentary origin, accumulated originally at the bottoms of ponds, lakes, and in the sea.
Tripoli and rottenstone are light, porous, siliceous rocks which have resulted from the leaching of calcareous materials from various siliceous limestones or calcareous cherts in the process of weathering.
Grinding pebbles are derived from the erosion of limestone or chalk formations which contain concretions of extremely fine-grained and dense chert. Under stream and wave action they are rounded and polished. The principal sources are ocean beaches.
Corundum as an abrasive is the mineral of this name—made up of anhydrous aluminum oxide. Emery is an intimate mechanical mixture of corundum, magnetite, and sometimes spinel. Corundum is a product of contact metamorphism and also a result of direct crystallization from molten magma. Canadian corundum occurs as a constituent of syenite and nepheline-syenite in Lower Ontario. In North Carolina and Georgia, the corundum occurs in vein-like bodies at the contact of peridotite with gneisses and schists, and also in part in the peridotite itself. In New York the emery deposits are segregations of aluminum and iron oxides in norite (a basic igneous rock). The emery of Greece and Turkey occurs as lenses or pockets in crystalline limestones, and is the result of contact metamorphism by intrusive granites.
Garnets result mainly from contact metamorphism, and commonly occur either in schists and gneisses or in marble. The principal American occurrences are of this type. Being heavy and resistant to weathering, they are also concentrated in placers. The Spanish garnets are reported to be obtained by washing the sands of certain streams.
Pumice is solidified rock froth formed by escape of gases from molten igneous rocks at the surface. It is often closely associated with volcanic ash, which is also used for abrasive purposes.
In general, the geologic processes entering into the formation of abrasives cover almost the full range from primary igneous processes to surface alterations and sedimentation.
The principal uses of asbestos are in high-pressure packing in heat engines, in thermal and electrical insulation, in fire-proofing, and in brake-band linings.
The largest producers of asbestos are Canada (Quebec) and, to a considerably less extent, Russia. United States interests have financial control of about a fourth of the Canadianproduction, and practically the entire export trade of Canada goes to the United States. Russia exports nearly all her product to Germany, Austria, United Kingdom, Belgium, and the Netherlands. Previous to the war the output was largely controlled by a German syndicate. There is a considerable recent production in South Africa, which is taken by England and the United States, and small amounts are produced in Italy, Cyprus, and Australia.
The United States has been a large importer of asbestos, from Canada and some other sources. Domestic production is relatively insignificant, and exports depend chiefly on an excess of import. Georgia is the principal local source. Arizona and California are also producers, their product being of a higher grade. The United States is the largest manufacturer of asbestos goods, and exports go to nearly all parts of the world.
So long as the abundant Canadian material is accessible on reasonable conditions, the United States is about as well situated as if independent. Some Canadian proposals of restriction during the war led to a study of other supplies and showed that several deposits, such as those in Russia and Africa, might compete with the Canadian asbestos.
Asbestos consists mostly of magnesium silicate minerals—chrysotile, anthophyllite, and crocidolite. The term asbestos covers all fibrous minerals with some tensile strength which are poor conductors and can be used for heat-protection. Like talc, they are derived principally from the alteration of olivine, pyroxene, and amphibole,—or more commonly from serpentine, which itself results from the alteration of these minerals. Chrysotile is the most common, and because of the length, fineness, and flexibility of its fibers, enabling it to be spun into asbestos ropes and fabrics, it is the most valuable. Anthophyllite fibers, on the other hand, are short, coarse, and brittle, and can be used only for lower-grade purposes. Crocidolite or blue asbestos is similar to chrysotile but somewhat inferior in fire-resisting qualities.
Asbestos deposits occur chiefly as veinlets in serpentine rock, which is itself the alteration of some earlier rock like peridotite. They are clearly formed in cracks and fissures through the agencyof water, but whether the waters are hot or cold is not apparent. The veinlets have sometimes been interpreted as fillings of contraction cracks, but more probably are due to recrystallization of the serpentine, proceeding inward from the cracks. In Quebec the chrysotile asbestos (which is partly of spinning and partly of non-spinning grade) forms irregular veins of this nature in serpentine, the fiber making up 2 to 6 per cent of the rock.
In Georgia the asbestos, which is anthophyllite, occurs in lenticular masses in peridotite associated with gneiss. It is supposed to have formed by the alteration of olivine and pyroxene in the igneous rocks. In Arizona chrysotile is found in veins in cherty limestone, associated with diabase intrusives. Here it is believed to be an alteration product of diopside (lime-magnesia pyroxene) in a contact-metamorphic silicated zone.
Crocidolite is mined on a commercial scale only in Cape Colony, South Africa. The deposits occur in thin sedimentary layers interbedded with jaspers and ironstones. Their origin has not been worked out in detail.
The deposits of Russia, the Transvaal, Rhodesia, and Australia are of high-grade chrysotile, probably similar in origin to the Quebec deposits. The asbestos of Italy and Cyprus is anthophyllite, more like the Georgia material.