The Economic Aspect of Geology Part 20

The oxides of zirconium have high refractory properties which make them useful for refractory bricks and shapes for furnace linings, for chemical ware, and for other heat, acid, and alkali resisting articles.

For these purposes they find a limited market. Experimental work seems to show possibilities of a very considerable use of zirconium as a steel alloy; indeed, results are so suggestive that during the war the government conducted an active campaign of investigation with a view to using it in ordnance and armor steel. For such purposes the alloy ferrozirconium is used, which carries 25 to 35 per cent zirconium metal.

The princ.i.p.al known deposits of zirconium ores, in order of commercial importance, are in Brazil, in India, and in the United States (Pablo Beach, Florida). The Brazilian and Indian deposits are also the princ.i.p.al sources of mon.a.z.ite (pp. 288-289). The United States controls one of the important Brazilian deposits. Germany before the war controlled the Indian deposits, and is reported to have taken much interest in the development of zirconium steels. During the war German influence in India was effectively broken up. The use of zirconium has been in an experimental state, and known sources of supply have been ample for all requirements.

GEOLOGIC FEATURES

The zirconium silicate, zircon, is a fairly common accessory const.i.tuent of granitic rocks and pegmat.i.te veins. From these rocks it is separated by weathering, disintegration, and stream transportation, and, having a high specific gravity, it becomes concentrated in placers. The deposits of southern India, of the coast of Brazil, and of Pablo Beach, Florida, all contain zircon along with ilmenite, garnet, rutile, mon.a.z.ite, and other insoluble, heavy minerals, in the sands of the ocean beaches.

Smaller deposits of zircon-bearing sands exist in rivers and beaches in other parts of the United States and in other countries, but none of these deposits has thus far proved to be of commercial importance.

The largest and most important zirconium deposits are on a mountainous plateau in eastern Brazil and are of a unique type, entirely different from those just described. They contain the natural zirconium oxide, baddeleyite or brazilite, mixed with the silicate, the ore as produced carrying about 80 per cent zirconia (ZrO_{2}). The ores consist both of alluvial pebbles and of extensive deposits in place. The latter are a.s.sociated with phonolite (igneous) rocks, and seem to owe their origin to the agency of hot mineralizing solutions from the igneous rocks.

t.i.tANIUM ORES

ECONOMIC FEATURES

t.i.tanium is sometimes used in steel manufacture to take out occluded gases and thus to increase the strength and wearing qualities. Its effect is to cure certain evils in the hardening of the molten steel, and it is not ordinarily added in amounts sufficient to form a definite steel alloy. Aluminum is frequently used in place of t.i.tanium. t.i.tanium is added in the form of ferrot.i.tanium, containing either about 15 per cent t.i.tanium and 6 to 8 per cent carbon, or about 25 per cent t.i.tanium and no carbon. t.i.tanium compounds are also used in pigments, as electrodes for arc-lights, and by the army and navy for making smoke-clouds.

The United States has domestic supplies of t.i.tanium sufficient for all requirements. Production has come chiefly from Virginia. Additional quant.i.ties have been imported from Canada and Norway. The recently developed deposits of Pablo Beach, Florida, may produce important amounts of t.i.tanium minerals along with the output of zircon and mon.a.z.ite.

GEOLOGIC FEATURES

The princ.i.p.al t.i.tanium minerals are rutile (t.i.tanium oxide) and ilmenite (iron t.i.tanate). These minerals are formed mainly under high temperatures, either during the original solidification of igneous rocks, or as const.i.tuents of the pegmat.i.tes which follow the crystallization of the main igneous ma.s.ses. The Virginia production comes from pegmat.i.te dikes cutting through gabbros, syenites, and gneisses. The deposits contain rutile in amounts as high as 30 per cent of the ma.s.s, but averaging 4 or 5 per cent, in addition to varying amounts of ilmenite. t.i.taniferous magnet.i.tes, formed in many basic igneous rocks by the segregation of certain iron-bearing materials into irregular ma.s.ses, contain large quant.i.ties of ilmenite which are not commercially available under present metallurgical processes.

Rutile and ilmenite both have high specific gravity and are little affected by weathering. Consequently they are not decomposed at the surface, but when carried away and subjected to the sorting action of streams and waves, they form placer deposits. Both of these minerals are recovered from the sands at Pablo Beach, Florida.

MAGNESITE

ECONOMIC FEATURES

The most important use of magnesite is as a refractory material for lining furnaces and converters. It is also used in the manufacture of Sorel cement for stucco and flooring, in making paper, in fire-resisting paint, in heat insulation, and as a source for carbon dioxide. Small amounts are used in Epsom salts and other chemicals.

As taken from the ground the ore consists princ.i.p.ally of the mineral magnesite or magnesium carbonate, with minor impurities (1 to 12 per cent) of lime, iron, silica, and alumina. In making magnesite bricks, it is calcined or "dead-burned" to drive out the carbon dioxide.

Austria-Hungary and Greece are the large European producers of magnesite and Scotland supplies a little. Most of the European production is consumed in England and the Central European countries, but part has been sent to America. Outside the United States there are American supplies in Canada, and recent developments in Venezuela and Mexico (Lower California).

Magnesite is produced in considerable quant.i.ties in the United States, in California and Washington. Some material is imported from Canada, and a small amount comes from Scotland as return cargo for ballast purposes.

Before the war only about 5 per cent of the United States requirements of magnesite were met by domestic production. The country was practically dependent on imports from various European countries; chiefly from Austria-Hungary and Greece The Austrian magnesite (controlled in large part by American capital) was considered especially desirable for lining open-hearth steel furnaces, because of the presence of a small percentage of iron which made the material slightly more fusible than the pure mineral. When the shipments from this source were discontinued during the war and prices rose to a high figure, experiments were made with American magnesite, and the deposits on the Pacific Coast were developed on a large scale. A process of treatment was perfected by which the Washington magnesite was made as desirable for lining furnaces as the Austrian material. At the same time large amounts were imported from Canada and Venezuela and lesser amounts from Lower California.

Under the high prices which prevailed during the war, dolomite was to some extent subst.i.tuted for magnesite. Dolomite, which may be thought of as a magnesite rock high in lime, occurs in large quant.i.ties close to many points of consumption. It is cheaper but less satisfactory than magnesite, and is not likely to be used on any large scale.

While the United States has undoubtedly sufficient reserves of magnesite to supply the domestic demands for many years, the mines are far from the centers of consumption and it is expensive to transport the material. Since the war, magnesite shipped from Canada and overseas has again replaced the American product in the eastern market to some extent. The Canadian magnesite is of lower grade than the domestic and European magnesite and is consequently less desirable. Deposits in Venezuela are also expected to furnish some material for the eastern furnaces, in compet.i.tion with those of Austria and Greece. Austrian magnesite, however, will be likely to dominate the market in the future if delivered at anything like pre-war prices. This situation has led to agitation for a protective tariff on magnesite.

GEOLOGIC FEATURES

Magnesite, as noted above, is the name of a mineral, the composition of which is magnesium carbonate. The princ.i.p.al magnesite deposits are of two types, of different modes of origin and of somewhat different physical characteristics.

The large magnesite deposits of Austria and of Washington, as well as those of Quebec, occur as lenses in beds of dolomite (calcium-magnesium carbonate). They are in fairly close proximity to igneous rocks, and magnesia-bearing solutions issuing from these rocks are believed to have dissolved out the calcium carbonate of the dolomite and replaced it with magnesium carbonate. In these deposits the material is coa.r.s.ely crystalline and forms fairly large, continuous bodies, which are worked by quarrying. The Washington deposits closely resemble marble, and had sometimes been mistaken for that rock until war-time needs resulted in their more thorough investigation.

The commoner type of magnesite deposits is represented by those of Greece, California, Venezuela, and many other countries. These consist of veins and replacements in serpentine. The original rock was a highly magnesian igneous rock of the peridot.i.te type, which is very unstable under weathering conditions, and rapidly alters to serpentine. Magnesite is formed both by this process and by the further breaking down of the serpentine itself. The processes are those of katamorphism. Under these circ.u.mstances the magnesite is characteristically fine-grained or ma.s.sive, and occurs in veins, lenses, and irregular bodies in cavities and fractured zones. It is usually worked by open cuts.

Magnesite is also reported to occur in sedimentary beds in which it was primarily deposited in its present form and has not undergone later alteration. Such deposits are not important commercially.

FLUORSPAR

ECONOMIC FEATURES

The chief use of fluorspar is as a flux in the manufacture of open-hearth steel. Minor uses are in chemical and enameling industries, in the smelting of copper, lead, and iron, and in the manufacture of the ferro-alloys in the electric furnace.

In order to be used in steel-making, the fluorspar after being concentrated should contain at least 85 per cent calcium fluoride and less than 4 per cent silica. Chemical and enameling industries require material with 95 to 98 per cent calcium fluoride and less than 1 per cent silica.

The chief foreign producer of fluorspar is Great Britain, and much of this product comes to the United States. Canada produces a small amount, some of which also comes to the United States. Several thousand tons are produced yearly in Germany and France, and are largely consumed there.

The production of fluorspar in the United States is several times that of any other country. The ore mined comes princ.i.p.ally from the southern Illinois and western Kentucky field, and is used largely for fluxing purposes in open-hearth steel furnaces. Minor amounts are produced in Colorado, New Mexico, and other states.

The United States has sufficient supplies of fluorspar to meet all its own demands for this material. Small amounts, however, are imported for use in eastern furnaces because the material can be brought over from England very cheaply. The domestic fluorspar is suitable for practically all purposes for which fluorspar is used except for lenses in optical instruments. For this use very small quant.i.ties of material imported from j.a.pan have been used, but recently fluorspar of a grade suitable for optical purposes has been found in Illinois, Kentucky, New Hampshire, and other states. For fluxing purposes domestic fluorspar is superior to the foreign product.

GEOLOGIC FEATURES

Fluorspar is the trade name for the mineral fluorite, which is composed of calcium fluoride. This is a common mineral in veins and replacements which carry ores of zinc, lead, silver, gold, copper, and tin. It is formed under a variety of conditions, but is always ascribed to solutions coming from nearby igneous rocks.

The large fluorspar deposits of Illinois and Kentucky contain fluorite with calcite, barite, and metallic sulphides, in wide veins filling fissures in limestones and sandstones and replacing the fissure walls.

Into these sediments there are intruded certain peridot.i.te dikes. The fluorite and a.s.sociated minerals were probably deposited by hot solutions bringing the material from some large underlying igneous ma.s.s of which the dikes are off-shoots.

In the western United States many metalliferous deposits carry large amounts of fluorite, which is treated as a gangue or waste mineral, but which could be profitably extracted if there were local markets. In England, fluorite is obtained in this manner as a by-product from lead and zinc mines.

SILICA

ECONOMIC FEATURES

Silicon and its oxide, silica, find important applications in the manufacture of iron and steel. Silicon, like manganese, is an important const.i.tuent of many steels, the alloy ferrosilicon being added to deoxidize and purify the metal and thus to increase its tensile strength. Like t.i.tanium, it is added chiefly for its curative effect rather than as a useful ingredient. On an average 4 pounds of 50 to 55 per cent ferrosilicon are used in the United States for each ton of steel produced. A higher grade of ferrosilicon (80 to 85 per cent) is used for certain special steels, and during the war considerable quant.i.ties were used in making hydrogen gas for balloons. Lower grades (10 to 15 per cent silicon) are practically a high silicon pig iron.

Silica has an important use in the form of silica brick or "ganister"

for lining furnaces and converters in which acid slags are formed. For this purpose siliceous rocks, chiefly quartzites and sandstones, are ground up, mixed with lime as a binder, and fused and pressed into bricks and shapes. For the most satisfactory results the rock should contain 96 per cent or more of silica, and very little of the alkali materials, which increase the fusibility.

In addition to its applications to the iron and steel industry, silica finds an almost universal use in a wide variety of structural and manufacturing operations. The extensive use of sand and gravel--composed chiefly of silica--for road materials and railway ballast is well known.