Economic Ores and Minerals


Aluminum is derived from two ores, cryolite and bauxite. This metal has made rapid strides into favor during the past half-dozen years. Although known since 1827, it remained a rare substance in the metallic form, though it is the most abundant of any of the metals in its ore. In ordinary clay there is an inexhaustible source of aluminum. But the ores that yield the metal cheaply are few. Until recently, cryolite, found abundantly in Greenland, was the chief source of the metal, but now bauxite is used in its place. Bauxite is a limonite iron ore in which a part of the iron has been replaced by aluminum. It is found in Alabama, Georgia and Arkansas, as well as in Europe. Aluminum is white, and very light in weight. It does not tarnish easily.

The chemical composition of these ores is:

In 1895 the production of this metal in the United States was 900,000 pounds. In 1899 it rose to 6,500,000 pounds. The only firm producing aluminum is the Pittsburg Manufacturing Company of Buffalo, N.Y., who reduce the metal from bauxite, which they obtain in the southern states. One of the latest uses for this metal is for gold miners' pans. The French seem to keep ahead of the rest of the world in finding new uses for aluminum.


Most of the supply of cryolite comes from Greenland, where it occurs in veins running through gneiss rocks. Glass-makers use it and pay good prices for it. Lately makers of aluminum also buy it, as it contains 13 per cent. of that metal.

A new aluminum-bearing mineral, discovered in New Mexico and in Ohio, is called native alum. It gives 50.16 per cent. alumina, and may be treated by solution in warm water, filtration, evaporation and roasting. No estimate has yet been made of the amount available.

As bauxite promises to be in greater demand in the future than in the present, owing to the ever-increasing demand for aluminum, the prospector will do well to make himself thoroughly familiar with its appearance. It is creamy white when free from iron, and the grains are like little peas, or pisolitic. It contains water, aluminum, silica, and generally iron. The French beds near the town of Baux are 30 miles long and 40 feet thick. In the United States, beds have been found in Alabama, Georgia and Arkansas. The Georgia beds are turning out three-fifths of the bauxite produced in America. The ore is in beds and pockets, and enough has been prospected to assure a supply for some years to come, unless the demand should grow very decidedly, in which case a scarcity might soon be felt. The American ore is easier to work than the French, and manufacturers prefer it to any they can import, even though the cost is higher and the percentage of aluminum smaller. The Arkansas deposits are as thick as the French, and only 300 feet above the level of the tide. Imported bauxite cost $5 to $7 a ton in New York City. American ore costs $5 to $12 a long ton. Best selected Georgia brings $10.

Should the deposits of bauxite give out, the manufacturers of aluminum would probably fall back on cryolite. At Tvigtuk, on the west coast of Greenland, it exists, as a very heavy vein, in gneiss. It is semitransparent, and snow-white. Impurities may stain it yellow or red or even black. Its specific gravity is 2.95, and its hardness 2.5 to 3. It is fusible in the flame of a candle, and yields hydrofluoric acid if treated with sulphuric acid. It is still used for making soda and aluminum salts, and an imitation porcelain. It is also in general use as a flux.

Amber. This is a fossil resin, or gum, and may often be found in lignite beds. Recent discoveries have been made on the coast of British Columbia that are expected to supply the world. All pipe-smokers know it.

Antimony. The commercial ore of this metal is the sulphide known as stibnite, or gray antimony. Its composition when pure is 72 per cent. antimony and 28 per cent. sulphur. Hardness is 2; gravity, 4.5; luster, metallic; opaque; gray; cleavage, perfect. Fracture, conchoidal. Texture, granular to massive. The ore tarnishes quickly, is easily melted, or dissolved in hydrochloric acid. The associated minerals are generally the ores of lead, zinc, and carbonate of iron. Baryta may be the gangue or veinstone. Antimony is worth from 10 to 15 cents a pound.

Although antimony occurs in many minerals, the only commercial source is the sulphide, stibnite. Antimony is used as an alloy in type metal, pewter, and babbitt metals. It is injurious to copper, even one-tenth of one per cent. reducing the value of that metal very considerably. The price varies greatly, being now about 10 cents a pound.

The composition of stibnite is:

The production of antimony in this country is not very large. The output of 1899 was but 1,250 tons, valued at $241,250. The ore is worth from $40 to $50 a ton delivered at Staten Island, N.Y.

Apatite suffered in demand when the cheap phosphates of South Carolina were discovered, and these in turn are being ousted from the markets of the world by Thomas slag, an artificial phosphate, and by the easily-mined natural phosphates of Algeria. The price varies with the quality of the rock, from $1.75 to $11 per ton, averaging in 1899, $3.86.

Apatite is a phosphate of lime, containing 43 per cent. of phosphoric acid. It occurs in the old crystalline and primary rocks of Canada, but although still of some value it has yielded the position it once occupied to the Carolina phosphate deposits, which, although not so rich in acid, are softer, and less expensive to utilize. Apatite is doubtless derived from the remains of animals or fishes that lived in the distant past. The colors are often beautiful--green, pink, gray, etc.--but the sheen is always white. Hardness of 4.8. Specific gravity, 3.1.

Asbestos. This fibrous silicate of magnesia and lime is to be looked for among primary rocks near serpentine dike. The fibers of this material may be woven into cloth that will be fire-proof. It is of considerable, though fluctuating, value.

The demand for this material is likely to increase, though at present the supply is fully equal to demand. It is being used in Germany to make fire-proof paper, and in Quebec to make asbestos plaster for covering wood-work. It is generally quarried in open pits, the rock being crushed in a rock-breaker, and the fiber freed from adhering particles of rock and dust. It is then sorted, the longest fibers going into the first quality heap. The production in 1899 in the United States was 912 tons, value $13,860; in Canada, 23,266 tons, value $598,736.

Borax. This mineral is borate of soda. Its composition is: 37 per cent. boric acid, 16 per cent. soda, and 47 per cent. water. Its gravity is 1.7. Hardness, 2.3. It is white, and has a sweetish taste. Borax is valuable, but occurring as it does as an incrustation upon the ground over large areas, a detailed description would be superfluous, as the explorer will surely recognize it should he find it.

Clay. A good bed of clay may be of value in an accessible region. Brick-clay contains silica, alumina, iron, etc. Potters' clay is made by suspending ordinary brick-clay in water, and running off the water and fine particles suspended therein. These are allowed to settle, and, when dry, are fine potters' clay. The better the clay, the larger the percentage of potters' clay. Fire-clay should contain 60 per cent. of silica, and 30 per cent. of alumina. Mixed with sand and burnt into bricks, it will resist great heat. Light-colored clays are preferable for this purpose, as iron is prejudicial to a good fire-brick. Kaolin is the finest porcelain clay, and the best comes from China, Japan or France. It is a product of decay in feldspar rocks. The potash is washed out, and the silica and alumina left as parts of a white clay of fine grain.

Coal. Anthracite is bituminous coal that has been subjected to great heat and pressure; in plain language, baked. It contains over 90 per cent. of carbon. Specific gravity 1.5 to 1.8. Hardness, 2.3 to 2.6. The ash left after burning is white or red. There is little or no sulphur in anthracite. It does not coke.

There are three main divisions of coal, arranged according to their carbon, water and ash. They are:

               Carbon.       Water.         Ash.
Anthracite    80-95 p.c.     2-3  p.c.    4-10 p.c.
Bituminous    45-80 p.c.     1-5  p.c.    8-20 p.c.
Lignite        7-45 p.c.    15-36 p.c.    6-40 p.c.

Good bituminous coal contains about 85 per cent. of carbon, but the composition varies greatly. Cannel coal is a variety of bituminous that gives off much gas. It burns with a bright flame in an open grate, igniting as easily as a candle. Lignite is intermediate between coal and peat. All the Rocky Mountain coals are lignites. It is a very inferior coal at its worst, while at its best it is nearly the equal of a poor bituminous coal.

Some coals will coke and others will not; nothing but a trial can settle this matter in each individual case. Good coking coal is very valuable.

Cobalt. Cobalt ores are always found in veins with other metals. Pure cobalt is extremely rare. Cobalt colors are used for porcelain painting, glass-staining, etc.

Chromium. All chrome is obtained from chromite, which contains 68 per cent. of chrome sesqui-oxide, the remainder being iron protoxide. Hardness, 5.5; gravity, 4.4; luster, sub-metallic; opaque. Steel-gray to almost black. Harsh. Brittle. Cleavage, imperfect. Fracture, uneven. Texture, massive to granular. Chromite in gravel looks like shot. Serpentine often contains it, when it is apt to resemble a fine-grained magnetite. It is used chiefly in iron and steel alloys, and in making armor plate. It is also used in dyeing fabrics and in paint manufacture. But little chrome ore is produced in the United States. The importation in 1899 was 15,793 tons, value $18.03 per ton.

Chromite, FeOCr{?page_id {}2{?page_id }}O{?page_id {}3{?page_id }}      47-68

This ore is merchantable at $22 to $25 per ton.

Domestic ore ranges from $10 to $12 a ton, while the pure imported ores are worth $21 a ton. The yearly consumption in the United States is about 16,000 tons, and the American production 100 tons. This ore is useful as a lining for furnaces, and the demand promises to become important. Newfoundland is said to contain large deposits.

Copper. Native copper occurs in the Lake Superior region, but the demands of commerce are supplied from chalcopyrite or copper pyrites, and tetrahedrite or gray copper ore. Many different ores of copper may exist in the same vein. On the surface an iron cap of gossan reveals the deposit; immediately below may be black oxide of copper with some malachite, lower down red oxide, and below the water-line copper sulphides. The following are the principal copper ores:

               Sp. Gravity.   Hardness.   P. C. Cu.
Native copper      8.8          2.8         100
Chalcopyrite       4.2          3.7          35
Enargite           4.4          3.0          48
Tetrahedite        5.0       3.5 to 4.5      35
Chalcocite         5.6          2.7          80
Bornite            5.0          3.0          55
Melaconite         6.2       2.0 to 3.0      80
Cuprite            6.0          3.6          89
Chrysocolla        2.2          3.0          45

The common ore is native copper, often associated with native silver, the two remaining, chemically, quite distinct. Some masses of copper occur that are too large to handle and must be cut by cold chisels, a method that costs more for labor than the value of the metal. The Lake Superior mines produce 140,000,000 pounds of copper a year, while those of Montana made the gigantic output of 228,000,000 pounds in 1896. The great Anaconda mine, of Butte, is the heaviest producer, yielding more than half the state's total.

During 1899 the New York copper market rate varied between 14.75 cents and 18.46 cents per pound. Copper is probably abundant in the shape of pyrites in many parts of Canada, especially in the Northwest, and prospectors in that region should search diligently for it. The Lake Superior mines are unique in being deposits of native copper.

Owing to the great demand for copper following upon the extraordinary spread of electricity, copper properties have become so enormously valuable that, possibly, the explorer will be quite as fortunate in finding copper as in finding gold. Moreover, with the exception of Spain and Chili, the United States has no serious rivals in copper production,--Montana and Michigan, producing the greater part of the output. The famous Calumet and Hecla mine, in Michigan, is now down 4,000 feet and still yields ore. The most copper ores are not difficult to distinguish. Every one is familiar with the ruddy hue of pure copper, the color of the native metal. It may be flattened under the hammer or cut with the knife. A little of the ore mixed with grease colors a flame green. Copper ores are heavy, and generally of a bright color, either red, blue, green, yellow or brown.

Corundum. Nine hundred and seventy tons of this abrasive were produced in the United States in 1899; value, $78,570. Corundum is found in feldspar veins, and associated with chlorites in serpentine rock. North Carolina furnishes half the corundum marketed. The presence of this substance is always indicated in the South by serpentine, chrysolite, or olivine rocks; experience being the only guide the miners have in finding new deposits. The contacts of the olivine rocks with gneiss usually produce rich deposits. Corundum is the hardest substance known, next to the diamond. It is used as a polishing powder. Emery is an impure corundum containing iron. Corundum is composed of 53 per cent. aluminum and 47 per cent. oxygen. Specific gravity is 4. Hardness, 9.

Feldspar. The Maine, Pennsylvania, New York, and Connecticut ores are worth $3 to $6 per long ton (2,240 pounds) at point of production.

Fluorspar. The American market is supplied by ore from Rosiclare, Ill., Marion, Ky., Hardin Co., Ill., and Liumpton Co., Ky., and imported spar. It is worth $6 a ton of 2,000 pounds. This spar is softer than quartz and of most brilliant colors, varying through the yellows, greens, blues and reds, to pure white. The streak is always white. Specific gravity, 3. Hardness, 4. It is worth mining when abundant and accessible.

Gems. Gems are to be looked for in a country of crystalline rock, such as granite, gneiss, dolomite, etc. Topaz and ruby are generally discovered in crystalline limestones, while turquoise is usually found in clay slate. It is not likely that the American prospector will come upon the true oriental ruby; he will more probably find the garnet. The ruby is next to the diamond in hardness and in value, and consists practically of pure alumina. The garnet is but as hard as quartz, and is a silicate of alumina with lime and a little iron. They crystallize in different systems, the more valuable gem belonging to the rhombohedral, and the less valuable to the isometric system.

The turquoise which has lately been found in Arizona is not a crystal. The blue color which distinguishes it is derived from copper. It is a phosphate of alumina with water in composition. In form it is kidney shaped or stalactitic. Lazulite, a far less valuable substance, is also blue, but as it crystallizes in the monoclinic system it should not be mistaken for turquoise. Moreover, lazulite is softer and contains magnesia and lime, which the turquoise does not. Lapis lazuli, which is also occasionally mistaken for turquoise, belongs to the regular or isometric system; it is commonly massive or compact, and is a silicate of alumina with some lime and iron. It is found in syenite, crystalline, limestone, and often associated with pyrites and mica.

Topaz belongs to the orthorhombic system. It is a silicate of alumina with fluorine. Powdered, mixed, and heated with microcosmic salt in the open tube, fluorine is disengaged with its characteristic odor, and etching action upon glass. With the blow pipe on charcoal, heated with the cobalt solution, it gives the fine blue color of alumina.

The explorer who comes upon any hard, brightly colored stone, that may possibly turn out a gem, should preserve it carefully until he returns to some city, when it should be submitted to an expert. The value of a gem depends upon so many qualities that it were hopeless for the tyro to endeavor to arrive at any just estimate of it. He might ruin a superb specimen, without becoming one bit the wiser. A few of the more prominent characters of valuable gems follow:

  Name.      Sp. Gravity.    Hardness.   Color.
Aquamarine        2.7          7.7     Blue.
Emerald           2.7          7.5     Green.
Diamond           3.5         10.0     Colorless.
Garnet            4.1          7.0     Claret.
Opal              2.2          6.0     Opaline.
Ruby              3.5          8.0     Dark red.
Tourmaline        3.1          7.3     Various.
Turquoise         2.7          6.0     Blue, green.
Ultramarine       2.5          5.8     Blue to green.

Graphite. This mineral is commonly known as black lead, or plumbago. It is the same in composition as the diamond, viz.: 100 per cent. carbon. Specific gravity, 2 to 2.2. Hardness, 1.2 to 1.9. Color, black. Greasy. Of value when free from impurities. Used in making pencils, stove polish, crucibles, etc. Found in the earlier rocks.

Gypsum. A sulphate of lime occurring in great beds. Burnt, it becomes plaster of paris.

Iron. This, the most important of all metals, is found in various forms. The ores of iron are:

             Sp. Gravity.  Hardness.  P. C. Fe.
Native ore       7.7         4.5        100
Magnetite        5.1         6.0         72
Hematite         4.8         6.0         70
Limonite         3.8         5.2         60
Siderite         3.8         4.0         62
Pyrite           5.0         6.3         47

Native iron is only found in meteorites that have come from space.

Magnetite is loadstone ore; the powder is reddish black, and the ore, dark brown to black. It is found in the older rocks and is an important ore.

Hematite varies from metallic to dull in luster. There are many varieties of it, known as ironstone, ocher, needle ore, etc. Hematite may be slightly magnetic. Immense beds exist in the triassic sandstones, and in the secondary rocks below the coal measures. The powder and streak of limonite are always yellow; it is an important ore. Siderite assumes many forms. It is called spathic ore, clay-ironstone, carbonate of iron, black band, etc. Most of these carbonate iron ores only range between 30 and 40 per cent. of metallic iron, but are in demand as fluxes for other iron ores. The pyritic ores of iron, including marcasite, pyrrhotite and mispickel, are often taken for gold by the inexperienced. In an accessible region pyrites may be valuable, as they are bought by makers of sulphuric acid.

Iron is so low in price that vast deposits exist which cannot be made use of because they would be too expensive to mine. A deep bed, or a narrow one, or the slightest difficulty in transportation, would preclude any profitable development. It is known that enormous areas in northern Labrador, for instance, are full of iron deposits, yet there seems no chance of their having the slightest economic value for a long time, if ever. Conditions of commerce very different to those now obtaining will have to exist before they can be utilized.

Iron ore is most favorably situated for profitable extraction when it is near coking coal and beds of limestone; the former for fuel, the latter for flux. Occasionally such regions as that of Lake Superior may be able to compete successfully with others, although they do not possess the necessary smelting facilities, because these deficiencies are counterbalanced by inexhaustive stores of easily mined ores, and transportation facilities unrivaled in cheapness.

Lead. The two important sources of supply are galena and cerussite. The former contains 87 per cent. of lead, and frequently some silver and gold. It is so distinctive as to be easily recognized. Luster, metallic; opaque; lead-gray; harsh. Brittle to sectile (may be cut). Cleavage, perfect. Fracture, even to sub-conchoidal. Structure, granular or foliated, tabular, or fibrous. Specific gravity is 7.5, and hardness, 2.6.

The carbonate cerussite contains about 79 per cent. lead. Luster, vitreous to resinous. Translucent. Color, gray. Smooth. Brittle. Cleavage, perfect to imperfect. Fracture, conchoidal. Massive to granular. Rich carbonate ores look like clay, and are undoubtedly often passed by.

The economic ores of lead are:

Galena        PbS                                  86.6  p.c.
Cerussite     PbCO{?page_id {}3{?page_id }}                              77.5  p.c.
Anglesite     PbSO{?page_id {}4{?page_id }}                              67.7  p.c.
Pyromorphite  Pb{?page_id {}3{?page_id }}P{?page_id {}2{?page_id }}O{?page_id {}8{?page_id }} plus 1/3 PbCl{?page_id {}2{?page_id }}       75.36 p.c.

Lead ores are frequently rich in silver. They occur in limestone, sandstone, granite and clay. The commercial ores are galena, which is easily recognized by its steel-like cubes, and the carbonates. These latter are like lightly colored clays when in powder and are very apt to be overlooked. Fluor spar is as favorable a gangue for lead as quartz is for gold.

The Rocky Mountains are the principal American sources of this metal, but a very large amount comes from the Mississippi valley. In the mountains the ore is a by-product, in silver smelting, being obtained from argentiferous galena, while in Missouri, Kansas, Wisconsin and Illinois lead and zinc are found free from any mixture with the precious metal. The age of these deposits varies from lower silurian or cambrian to the carboniferous.

The ore is found in limestone rocks,--sometimes in flat openings parallel to the almost horizontal beds, or else in gash veins almost at right angles to these. As lead is often found in dolomite limestone, that is, limestone carrying almost as much magnesia as lime, and this rock was undoubtedly deposited in a shallow sea, geologists incline to the belief that therefore the lead is due to a growth of seaweeds in whose ash this metal and zinc are known to occur. At any rate, these deposits now have great economic value, and the lead and zinc ore is easily got at.

Galena and zinc blende frequently resemble one another, but they may be distinguished by this infallible sign: the powder of galena is black, and that of blende brown, or yellow.

Lithographic Stone. This is a very fine grained compact limestone from Bavaria. So far nothing equal to the imported stone has been found in America. The distinguishing qualities are: Gray, drab or yellow; porous, yet not too soft; of fine texture, and free from veins and inequalities.

Manganese. Manganese ores in 1899 amounted in the United States to 143,256 tons, value $306,476. This mineral is used for bleaching and making oxygen, and in steel manufacture. Pyrolusite contains 63 per cent. manganese. Hardness, 2.3. Specific gravity, 4.8. Luster, metallic. Opaque. Gray to bluish black. Harsh. Brittle. Cleavage, imperfect. Fracture, uneven. Granular, massive. Manganite is harder, 4.0; its specific gravity is 4.3. Luster, sub-metallic. Cleavage, perfect. Texture, fibrous. Wad is an impure ore of manganese found in bogs, of little or no value.

Pyrolusite      MnO{?page_id {}2{?page_id }}             63.2
Braunite        Mn{?page_id {}2{?page_id }}O{?page_id {}3{?page_id }}          69.68
Psilomelane     (Variable)           ?

Franklinite, a zinc-manganese ore, is also a common source of supply. An ore to be commercially valuable should contain from 40 to 60 per cent. metallic manganese, and not over 0.2 to 0.25 per cent. phosphorus.

To determine the value of manganese ores a somewhat intricate calculation is necessary. Delivered at Bessemer, Pa., the Carnegie Steel Company pays according to the following sliding scale:

Per cent.      Mn.     Per Unit
 over      49 p.c.     Fe.  Mn.
  46       49 p.c.     6c  28c
  43       46 p.c.     6c  27c
  40       43 p.c.     6c  26c
  37       40 p.c.     6c  25c
  34       37 p.c.     6c  24c
  31       34 p.c.     6c  23c
                       6c  22c

Moreover, for each one per cent. of silica in excess of eight per cent. a deduction of fifteen cents a ton is made, and a deduction of one cent per unit of manganese is made for each 2/100 of one per cent. of phosphorous present in excess of 1/10 per cent. From which it is evident that there can be little profit in impure deposits of manganese.

Mercury. Quicksilver usually occurs in the form of cinnabar, though occasional deposits of pure metal are found in drops and small pockets, in limestone and the softer secondary rocks, including shales and slates. As the appearance of quicksilver must be familiar to all, cinnabar alone needs description. Its specific gravity is 9.0; its hardness, 2.2. It is a red brown earthy ore, the powder of which is a dull red. It is generally found in sandstone, though it occasionally occurs in slates, shales and serpentine. Heated gently with lime cinnabar yields quicksilver. If copper be held over the fumes of mercury it will be coated with a light film of the metal. An alloy with silver has been found. Mercury is heavy, extremely brilliant, and mobile. The composition of cinnabar is:

                    Per cent. Hg.
Cinnabar HgS            86.2

Although but three American states have supplied this metal, this country has held rank as second producer. Of these California is by far the most important. Oregon and Utah having never had any but a small and spasmodic output. Judging by Californian experience, the prospector is most likely to find cinnabar, the ore from which the quicksilver of commerce is derived, in metamorphic rocks. Mercury is always sold in flasks of 76-1/2 pounds. The production of mercury by the United States (California) was 28,879 flasks in 1899, which were valued at $1,155,160.

The following table shows the rock in which the most famous Californian quicksilver mines are:

    Mine.       County.         Rock.
Sulphur Creek   Colusa       Serpentine.
Abbott          Lake         Shale-serpentine.
Great Western   Lake         Serpentine. (?)
Ætna            Napa         Sandstone.
Corona          Napa         Sandstone-serpentine.
Aat Hill        Napa         Sandstone.
New Almaden     Santa Clara  Shale-serpentine.
Barton          Siskiyou     Shale-sandstone.
Cinnabar King   Sonoma       Sandstone-serpentine.
Altoona         Trinity      Porphyry-serpentine.

A study of the foregoing shows that serpentine is almost as intimately connected with quicksilver as is quartz with gold, or granite with tin. These are the things that prospectors should make a note of. With the great increase of gold mining and the limited store of cinnabar that is available that ore seems certain to rise in value before long.

Mica. The value of Indian mica varies from 90¢ a pound for sheets 4 in. × 1 in. to $13 a pound for sheets 10 in. × 8 in. The white mica in large sheets is valuable. The amber-colored, and spotted, are used for insulating purposes in electric plants, while the coarser sorts are ground and used as lubricants, or in fire-proof paint manufacture.

Nickel. This ore is never found in metallic form, but always in combination. Pyrrhotite, or magnetic pyrites, is the source of about all the nickel of commerce. This ore has been already noticed under iron. Rare but valuable ores of nickel are millerite, nickelite, glance, and nickel bloom.

                      Per cent. nickel.
Millerite    NiS            64.4
Niccolite    NiAs           44.0

Some of the nickel of commerce is derived from nickelliferous pyrrhotite.

Petroleum. Crude petroleum is never found in metamorphic or igneous rocks. The stratified rocks of the Devonian, Carboniferous and Cretaceous ages are most likely to hold it. The crude oil is almost black, and consists of about 85 per cent. of carbon, and 15 per cent. of hydrogen. A long iron-shod stick is all the prospector requires to take with him in his search for surface indications of oil. The warmer the day the easier the search, as the oil rises to the surface of the streams, and is found in greater quantities than on cold days.

Oil existing in the lower rocks ascends through them until it accumulates under some layer that will not let it pass through. In this condition deep boring finds it, the rod usually tapping gas first. Petroleum may be noticed oozing out of gravel banks, or floating as a scum on the surface, whenever abundant. It has been found in rocks of widely different age, from extremely ancient formations to some that did not precede man by so very long, geologically speaking.

Platinum. This metal is only found native. Its gravity is very high, from 16 to 22. Hardness, 4 to 4.5. Luster, metallic. Opaque. Whitish-gray. Smooth. Ductile. Cleavage, none. Fracture, hackly. Texture, granular, fine. Platinum is unaffected by acids, but if alloyed with 10 per cent. of silver it dissolves in nitric acid. Almost infusible. Platinum occurs with placer gold in the beds of streams. Usually it is in small grains, but one or two large nuggets are on record from Brazil and Siberia. Serpentine rocks are believed to have originally held the platinum found in the beds of rivers, but none has been found in veins. The entire product of the United States was 300 ounces in 1898; valued at $3,837. In 1899 there was none produced.

Silver. Silver is generally found in serpentine, trap, sandstone, limestone, shale, or porphyry rocks, the gangue being quartz, calc, fluor, or heavy spar. All silver ores are heavy, and many of them are sectile, i.e., may be cut with the knife. Western men test for silver by heating the ore and dipping it into water. Some metal comes to the surface in a greasy scum, should silver be present. Native silver is found occasionally. Owing to the fall in value of this metal its future is not assured. It has fallen, during the past year, once to forty-nine cents an ounce, and this has had a most disastrous effect upon many silver mines, forcing them to suspend operations. Should the fall continue, as seems likely, and the price of silver go down to forty cents an ounce, little will be produced except as a by-product in the treatment of argentiferous lead ores.

As silver enters into chemical combination with sulphur easily, as is seen by the black film that forms on silver articles in a room where gas is burnt, most silver ores are sulphides. The very abundance of silver has caused its great fall in value, and it does not appear that it is ever likely to remain for long at a price exceeding fifty cents an ounce, owing to the ease with which it may be produced, and the large quantities that must find their way to market through it being a by-product in lead smelting. From 1859 to 1891 the Comstock lode in Nevada produced $325,000,000. This lode is a belt of quartz, 10,000 feet long and several hundred wide, and is a contact vein between diorite and diabase. In America galena is the principal source of silver; the chlorides and oxides rank next; while, lastly, some silver is parted from gold when it reaches the mint, as gold always contains more or less of that metal. No precise statement as to the manner of its occurrence may be made since it is found in many different positions, and is associated with all sorts of minerals. It is never found in placer deposits, as it breaks up under the influence of water, air, etc. Its original source is doubtless the igneous rocks, where it occurs in association with augite, hornblende and mica. Silver may be expected in mountainous regions of recent origin. Between 1875 and 1891 the world's product rose from $82,000,000 to $185,599,600. Three quarters of this came from the western hemisphere.

The commercial ores of silver are:

Argentite       Ag{?page_id {}2{?page_id }}S                  87.1 per cent.
Proustite       3Ag{?page_id {}2{?page_id }}SAs{?page_id {}2{?page_id }}S{?page_id {}3{?page_id }}        65.5 per cent.
Prysagyrite     3Ag{?page_id {}2{?page_id }}SSb{?page_id {}2{?page_id }}S{?page_id {}3{?page_id }}        59.9 per cent.
Stephanite      5Ag{?page_id {}2{?page_id }}SSb{?page_id {}2{?page_id }}S{?page_id {}3{?page_id }}        68.5 per cent.
Cesargerite     AgCl                    75.3 per cent.

The Anaconda mine in Butte is the largest producer of silver in the country. In 1896 its output was 5,000,000 ounces. The Anaconda is also the heaviest copper producer in the United States, its yield of copper being 125,350,693 pounds.

Sulphur. Brimstone is found native in the neighborhood of volcanoes, extinct or active. It is also derived from iron pyrites. Color, yellow. Hardness, 2. Specific gravity, 2. Luster, resinous. Smooth. Sectile. Texture, crystalline.

Talc. The scientific name of this mineral is steatite. It contains silica and magnesia. Its green color, pearly luster, and greasy feel, are very characteristic. It is not attacked by boiling sulphuric acid. Useful in the arts, but of no great value.

Tin. The composition of cassiterite, the commercial ore of tin, is SnO{?page_id {}2{?page_id }}; equal to 78.67 per cent. of metallic tin. Cassiterite or tin stone is a heavy ore which occurs in alluvial deposits or in the beds of streams. It will be one of the latest ores the young prospector will find himself able to name with certainty. Granite, with white mica as one of its constituents, has so far always been associated with tin. The American continent yields little tin, and it is not likely the prospector in either the western states or in Canada will stumble upon it, though a good deposit of stream tin would enrich him in a short time, for the metal is in great demand. The streak, when the metal is scratched with a knife point, is whitey-gray and very distinctive.

Tin may some day be found in the northern Rockies, as there is plenty of granite, which is favorable to this metal. It is worth about thirteen cents a pound, and a vein must yield more than five per cent. of metal to pay the cost of mining and dressing. Cassiterite, the principal tin ore, would have to be roasted. Most of the European tin mines were first worked for the copper they contained. The copper was found in the capping, but as they gained in depth they became more and more valuable for their tin. Some of the Cornish mines are three-quarters of a mile in depth. Very lately tin has been discovered and mined in vast quantities in the Straits Settlements, India. As it is found in the streams the expense of mining is very light, and it is killing the European mines. The Cornish miners put their tin ore on a shovel when they wish to test it. The sample is first crushed fine and a few skillful shakes get rid of all the gangue, leaving behind the tin and wolfram. This wolfram is always associated, in Cornwall, with the tin and it is got rid of by roasting. Australasia and Cornwall produce most of the tin used in commerce. Tin is not found native. Specific gravity of cassiterite is 6.5 to 7. Hardness, 6.5 to 7. Luster, vitreous to adamantine. Translucent to opaque. Brown, black, gray, red or yellow. Harsh. Brittle. Massive. The appearance of this metal is so variable that nothing but a test with reagents determines it with certainty. Granite is frequently the country rock in which tin is found.

Zinc. This is another ore that never occurs native. Calamine or silicate of zinc is the great producing ore. Composition: Zinc oxide, 67 per cent; silicate, 25 per cent; water, 8 per cent. Specific gravity, 3 to 3.7. Hardness, 4.6 to 5. Luster, vitreous. Translucent. White. Harsh. Brittle. Cleavage, perfect. Fracture, uneven. Texture, granular crystalline. Calamine is a difficult mineral to detect without experience, as when impure it does not look in the least like a metallic ore. It would be taken for clay or shale. This ore results from the decomposition of zinc blende. Blende contains 67 per cent. zinc and 33 per cent. sulphur. It is often dark brown or black from iron, otherwise it may be red, green or bluish. It is a troublesome impurity in silver ores. Smithsonite is a carbonate much resembling, and often found with, calamine. Other zinc ores are merely curiosities and do not affect the commercial value of the metal.

In the New Jersey mines the zinc ores are the oxides zincite and willemite, and the zinc-iron oxide franklinite. In the Missouri region, on the other hand, sphalerite and blende are the typical ores. Blende generally associates with the lead sulphide, galena. The Joplin district in southwestern Missouri and the adjoining region in Kansas are now mainly supplying the markets of the country, though the New Jersey deposits are very valuable.

Joplin ore assaying 58 to 62 per cent. has varied greatly in price during the past four years. The lowest quotation was $20 a ton, the highest $51.50.

Zinc is derived mainly from the following half dozen ores:

Sphalerite      ZnS                     67.0    per cent.
Zincite         ZnO                     80.3 per cent.
Smithsonite     ZnOCO{?page_id {}2{?page_id }}                51.9 per cent.
Franklinite     (Variable) (?)           5.54 per cent.
Willemite       2ZnO.SO{?page_id {}2{?page_id }}              58.5  per cent.
Calamine        2ZnO.SiO{?page_id {}2{?page_id }}.HO{?page_id {}2{?page_id }}       54.2  per cent.

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