Chapter III · THE MINERALS

KEY TO THE MINERALS, BASED ON HARDNESS, COLOR, ETC.

OPAQUE COLORS

Color Hardness Streak Remarks Mineral

Red

scarlet 2.5 scarlet surface tarnishes black prousite

2.5 vermilion surface scarlet to dark red cinnabar

ochre 7 white non-crystalline jasper

6 ochre red color red to almost black hematite

rose 4 white effervesces in warm acid rhodochrosite

dark 4 orange zincite

2.5 purplish red surface tarnishes black pyrargyrite

brownish 3.5 brownish red cuprite

Orange 3.5 white to yellowish pyromorphite

1-1½ orange realgar

Blue 5.5-6 white in igneous rocks sodalite

azure 4 azure azurite

sky 7 & 4.5 white blade-like crystals cyanite

turquoise 6 blue non-crystalline turquois

2-4 white chrysocolla

Green

malachite 3.5 lighter green malachite

olive 6.5-7 white in igneous rocks olivine

3.5 white to yellow pyromorphite

2 white mica-like cleavage chlorite

1 white greasy feel, color light to dark olive green talc

yellowish 6.5 white epidote

2.5-4 white color yellow green to olive serpentine

Yellow

golden 2.5 shining non-crystalline gold

brassy 6 greenish-black usually crystalline pyrite

6 greenish-gray color pale brassy yellow, usually non-crystalline marcasite

5.5 greenish-black colors nitric acid green millerite

4 greenish-black color golden similar to gold chalcopyrite

3.5 dark brown purplish tarnish on surface tetrahedrite

bronze 5.5 pale brownish-black color with coppery cast niccolite

4 dark gray-black with speedy black tarnish pyrrhotite

3 gray-black brownish with bluish tarnish bornite

2.5 shining coppery red color copper

sulphur 3.5 white to yellowish compact masses pyromorphite

2 yellow sulphur

1-3 earthy masses carnotite

Brown

violet 1½ shining tarnishes black cerargyrite

yellowish 7.5 white 4-sided prisms zircon

6.5 gray cassiterite

5.5 ochre yellow compact to earthy masses limonite

5 brownish-yellow goethite

4.5 black wolframite

3.5 yellowish-brown sphalerite

3.5 white siderite

grayish 7.5 white often twinned staurolite

6.5 pale brown rutile

3.5 white to yellowish earthy masses pyromorphite

reddish 7 white dodecahedrons & trapezohedrons garnet

Black 6.5 gray cassiterite

6 reddish-brown franklinite

6 black magnetic magnetite

5.5 dark brown chromite

5.5 black yellow precipitate in sulphuric acid wolframite

5-6 black non-magnetic ilmenite

5-6 brownish-black compact masses psilomelane

5 brownish-yellow surface often brownish goethite

3.5 dark brown tetrahedrons tetrahedrite

2.5 silvery fresh surfaces silver color silver

2.5 scarlet fresh surfaces bright red prousite

2.5 purplish red fresh surfaces red pyrargyrite

2 black earthy masses pyrolusite

1 steel gray greasy feel graphite

Metallic Gray 2.5 black tarnishes black, bluish, or green chalcocite

2.5 lead gray sectile argentite

2.5 lead gray cubic cleavage galena

2 lead gray long prismatic crystals stibnite

1.5 bluish gray in scales molybdenite

steel 5.5 gray black rose color in nitric acid smaltite

4.5 steel gray very heavy platinum

4 reddish black often in striated prisms manganite

1 gray with greasy feel graphite

silvery 5.5 black arsenopyrite

2.5 silvery tarnishes black on exposure silver

reddish 5.5 gray black rose color in nitric acid cobaltite

pearly 1-1½ shining exposed surfaces violet brown cerargyrite

White, with impurities 4 white porcelainous masses, effervesces in acid magnesite

grayish or yellowish 2 white earthy masses, greasy feel kaolinite

1-3 white earthy masses bauxite

1 white greasy feel, fibrous or scaly talc

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TRANSPARENT OR TRANSLUCENT COLORS

Color Hardness Remarks Mineral

Colorless or with faint tinges of color due to impurities

10 in octahedrons diamond

9 in hexagonal prisms corundum

8 in hexagonal prisms topaz

7 in three-sided prisms tourmaline

7 in hexagonal prisms quartz

7 non-crystalline chalcedony

7 or 4.5 cubes with beveled edges boracite

6 non-crystalline, pearly luster opal

5.5 rhombohedrons willemite

5.5 trapezohedrons analcite

5.5 tufts of needle-like crystals natrolite

5.5 sheaf-like bundles of crystals stilbite

5 hexagonal prisms with basal cleavage apatite

5 effervesces in acid smithsonite

5 becomes jelly-like in acid calamine

4.5 monoclinic prisms colemanite

4 in cubes fluorite

3.5 effervesces in acid, but one cleavage aragonite

3.5 effervesces in acid, heavy cerrusite

3 effervesces in acid, rhomboidal cleavage calcite

3 no effervescence, but soluble in nitric acid anglesite

2.5 in cubes tastes of salt halite

2 soluble in water, sweetish taste borax

2 1 perfect cleavage, and two imperfect cleaves at 66 with each other gypsum

White or with faint tinges of color due to impurities, such as pink, bluish, etc.

7 hexagonal prisms quartz

7 non-crystalline chalcedony

7 or 4.5 cubes with beveled edges boracite

6 non-crystalline, pearly luster opal

6 cleavage in 3 directions, good in 2 and imperfect in the other feldspar

5.5 short eight-sided prisms pyroxene

5.5 long six-sided prisms amphibole

5.5 trapezohedrons analcite

5.5 tufts of needle-like crystals natrolite

5.5 sheaf-like bundles of crystals stilbite

5.5 rhombohedrons willemite

5 effervesces in acid smithsonite

5 becomes jelly-like in acid calamine

4.5 & 7 cubes with beveled edges boracite

4.5 monoclinic prisms colemanite

4 effervesces in acid, porcelainous magnesite

3.5-4 effervesces in acid, heavy, red color in flame strontianite

3.5 effervesces in acid, heavy, green color in flame witherite

3.5 effervesces in warm acid, rhomboidal cleavage dolomite

3.5 effervesces in acid, cleavage in one direction only aragonite

3.5 effervesces in acid, heavy, does not color flame cerrusite

3-3.5 no effervescence, cleavage in three directions at right angles anhydrite

3 effervesces in acid, rhomboidal cleavage calcite

3 tabular crystals, heavy, green color in flame barite

2-3 cleaves in thin elastic sheets mica

2.5 cleaves in cubes cryolite

2.5 cubes, soluble in water, salty taste halite

2 1 perfect cleavage, and 2 less perfect ones gypsum

2 cleaves in thin non-elastic sheets chlorite

2 soluble in water, tastes sweet borax

1 greasy feel talc

Green 9 hexagonal prisms oriental emerald

8 octahedrons spinel

7.5 hexagonal prisms beryl

7 three-sided prisms tourmaline

7 dodecahedrons or trapezohedrons garnet

7 non-crystalline prase or plasma

6.5-7 non-crystalline, olive color olivine

6.5 yellow green color, rather opaque epidote

6 non-crystalline, pearly luster opal

5.5 short eight-sided prisms pyroxene

5.5 long six-sided prisms amphibole

5 hexagonal prisms apatite

4 cubes fluorite

3.5 effervesces in acid cerrusite

2.5-4 somewhat greasy feel, massive or fibrous serpentine

2 in mica-like scales, non-elastic chlorite

1 greasy feel, fibrous or scaly talc

Red 9 hexagonal prisms ruby

8 octahedrons spinel

7 three-sided prisms tourmaline

7 dodecahedrons or trapezohedrons garnet

7 hexagonal rose quartz

7 non-crystalline jasper or carnelian

6 pearly luster fire opal

4 cubes, rose tints fluorite

2-3 pink mica-like scales lepidolite

Blue 9 hexagonal prisms sapphire

7 & 4.5 blade-like crystals cyanite

6 non-crystalline masses turquois

5.5-6 in igneous rocks sodalite

4 azure color azurite

3.5 effervesces in acid, heavy cerrusite

2-4 earthy masses, turquoise color chrysocolla

Violet 7 hexagonal prisms amethyst

4 cubes fluorite

Yellow 9 hexagonal prisms oriental topaz

8 octahedrons spinel

8 hexagonal prisms topaz

4 cubes fluorite

Brown 9 hexagonal prisms corundum

8 octahedrons spinel

7.5 four-sided prisms zircon

7 hexagonal prisms smoky quartz

7 three-sided prisms tourmaline

7 non-crystalline flint

6 non-crystalline opal

5.5 short eight-sided prisms pyroxene

5.5 long six-sided prisms amphibole

2-3 cleaves into thin sheets mica

Black 9 hexagonal prisms corundum

8 octahedrons spinel

7 three-sided prisms tourmaline

5.5 short eight-sided prisms pyroxene

5.5 long six-sided prisms amphibole

2-3 cleaves in thin sheets mica

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The Gold Group

Gold was undoubtedly the first metal to be used by primitive man; for, occurring as it did in the stream beds, its bright color quickly attracted the eye, and it was so soft, that it was easily worked into various shapes, which, because they did not tarnish, became permanent ornaments. The metal is associated with the very earliest civilizations, being found in such ancient tombs as those at Kertsch in Crimea and in northern Africa and Asia Minor. It was used in the cloisonné work of Egypt 3000 years B.C. In America the Indians, especially to the south, were using it long before the continent was discovered.

Of all the metals gold is the most malleable, and its ductility is remarkable, for a piece of a grain’s weight (less than the size of a pin head) can be drawn out into a wire 500 feet long; and 30 it can be beaten into a thin leaf as thin as ¹/₂₅₀₀₀₀ of an inch in thickness, and thus a bit, weighing only a grain, can thus be spread over 56 square inches.

It forms very few compounds, but has a considerable tendency to make alloys (i.e., mixtures with other metals without the resulting compound losing its metallic character). In Nature gold is never entirely pure, but is an alloy, usually with silver, there being from a fraction of 1% up to 30% of the silver with the gold, the more silver in the alloy, the paler the color of the gold. Australian gold is the purest, having but about .3% of silver in it, while Californian gold has around 10% and Hungarian gold runs as high as 30% of silver. Another alloy fairly abundant in Nature is that with tellurium, such as calaverite (AuTe₂) which is a pale brassy yellow, similar to pyrite, but with the hardness of but 2.5. Another combination includes gold, silver and tellurium, sylvanite, (AuAgTe₄) a silvery white mineral with a hardness of but 2. Such combinations are known as tellurides and the calaverite is mined as a source of gold at Cripple Creek, Colo., while the sylvanite is one of the important ores of gold in South Africa. Occasionally gold is also found alloyed with platinum, copper, iron, etc. Jewelers make several alloys, “red gold” being 3 parts gold and 1 of copper, “green gold” being the same proportions of gold and silver, and “blue gold” being the combination of gold and iron. Our gold coins are alloys, nine parts gold and one of copper, to give them greater durability. Most of 31 the gold recovered from nature is found native, i.e., the pure metal, or with some alloy.

Gold Au Pl. 5

Usually non-crystalline, but occasionally showing cube or octahedral faces of the isometric system; hardness 2.5; specific gravity 19.3; color golden yellow; luster metallic; opaque.

Gold is mostly found as the metal and is readily recognized by its color, considerable weight, hardness, malleability, and the fact that it does not tarnish. It usually occurs in quartz veins in fine to thick threads, scales or grains, and occasionally in larger masses termed “nuggets.” It is insoluble in most liquids so that when weathered from its original sites, it was often washed down into stream beds, to be found later in the sands or gravels, or even in the sea beaches. When thus found it is termed “placer gold,” and its recovery is placer mining. Most of the original discoveries of gold have been in these placer deposits; and from them it has been traced back to the ledges from which it originally weathered. In the placer deposits the size of the particles varies from fine “dust” up to large nuggets, the largest found in California weighing 161 pounds; but the largest one found in the world was the “Welcome Nugget,” found in Australia, and weighing 248 pounds. When gold was discovered in California in 1848, this became the chief source for the world, but later this distinction went to Australia, and now belongs to South Africa, which today yields over half the annual supply.

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The ultimate source of gold is from the lighter colored igneous rocks, like granites, syenites, and diorites, throughout which it is diffused in quantities too small to be either visible or worth while to extract. It becomes available only when it has been dissolved out by percolating waters and segregated in fissures or veins, either in or leading from these igneous rocks. Generally this transfer of gold has taken place when the rocks were at high temperatures, and by the aid of water (and perhaps other solvents) which was also at high temperatures. The presence of gold in sandstones, limestones, etc., is secondary, as is also its presence in sea water, in which there is reported to be nearly a grain (about five cents worth) in every ton of water. Beside the direct recovery of gold from gold mining, a great deal is obtained from its association with iron, copper, silver, lead and zinc sulphides, in which it is included in particles too fine to be visible, but in quantities large enough to be separated from the other metals after they are smelted.

In the United States gold is found in the Cordilleran region from California to Alaska, in Colorado, Nevada, Arizona, Utah, the Black Hills of South Dakota, and in small quantities in the metamorphosed slates of North and South Carolina, Georgia, and in Nova Scotia.

The Silver Group

Though much commoner than gold, silver did not attract the eye of man as early, probably because it tarnishes when exposed to air or any other agent having sulphur compounds in it, 33 and a black film of silver sulphide covers the surface. Its first use was for ornaments, and some of these found in the ruins of ancient Troy indicate its use as early as 2500 B.C. A thousand years later it was being used to make basins, vases and other vessels.

Silver is next to gold in malleability and ductility, so that a grain of silver can be drawn out into a wire 400 feet long, or beaten into leaves ¹/₁₀₀₀₀₀ of an inch in thickness. As a conductor of electricity it is unsurpassed, being rated at 100% while copper rates 93%. Silver is also like gold in the freedom with which it alloys with other metals, such as gold, copper, iron, platinum, etc. All our silver coins, tableware, etc., have some copper alloyed with the silver to give it greater hardness and durability.

Unlike gold, silver freely enters into compounds with the non-metals, which is the reason that it is not found primarily in its native state, but usually as a sulphide. Its ultimate source is in the igneous rocks, few granites or lavas, on analysis, failing to show at least traces of silver. Before it is available as an ore, or mineral, it has been dissolved from the original magma, and segregated in fissures or veins, along with such minerals, as quartz, fluorite, calcite, etc. This seems to have taken place while the igneous rocks were still hot, and by the agency of vapors and liquids which were also hot. The presence of silver in sedimentary and metamorphic rocks, or even in sea water, is secondary.

The primary deposition of silver is usually in the form of sulphides, the commoner of which 34 are, argentite or silver sulphide, pyrargyrite or silver and antimony sulphide, and prousite, or silver and arsenic sulphide. Its occurrence as native silver, or the chloride, cerargyrite, is secondary and due to the reactions which have taken place when sulphide deposits have been subjected to weathering agents.

The United States produces about 25% of the world’s supply, Mexico some 35%. It is especially found along the Cordilleran ranges of both North and South America.

Silver Ag Pl. 6

Usually non-crystalline, but occasionally showing cube or octahedron faces of the isometric system; hardness 2.5; specific gravity 10.5; color silvery white; luster metallic; opaque.

When found in its native state silver is usually in wirey, flakey, or mossy masses; but sometimes masses of considerable size occur, the most famous being an 800 pound nugget found in Peru, and another of 500 pounds weight found at Konsberg, Norway, and now preserved in Copenhagen. When exposed to the air the surface soon tarnishes and takes on a black color which must be scraped off to see the real color.

Like gold, silver is usually found associated with other metals, like iron, copper, lead and zinc; and much of the silver recovered is obtained in connection with the mining, especially of copper and lead. Some lead ores have so much silver in them that they are better worth mining for the silver; galena, for instance, under such circumstances being termed argentiferous 35 galena. Native silver is a secondary mineral, having been formed by the reduction of some one of its sulphides by water, carrying various elements which had a greater affinity for the sulphur.

Silver is found along with copper in the Lake Superior region, and in Idaho, Nevada, and California.

Argentite AgS Pl. 6 silver glance

Usually in irregular masses, but sometimes in cubes; hardness 2.5; specific gravity 7.3; color and streak lead gray; luster metallic; opaque on thin edges.

Argentite, the simple sulphide of silver, is the chief source from which silver is obtained. It looks like galena, and has the same hardness, streak and specific gravity, but can be distinguished by the galena having a very perfect cubic cleavage while the argentite has no cleavage. Argentite is easily cut with a knife (sectile). It is usually found in irregular masses, but sometimes in cubes which make very choice cabinet specimens; and is associated with such other minerals as galena, sphalerite, chalcopyrite, pyrite, fluorite, quartz, and calcite.

It occurs in fissures and veins all through the Cordilleran regions, especially in California, Colorado, Nevada (Comstock Lode), Arizona (Silver King Mine) and about the shores of Lake Superior.

Pyrargyrite Ag₃SbS₃ Pl. 7 ruby silver or dark red silver

Usually occurs in irregular masses; hardness 2.5; specific gravity 5.8; color dark red to black; streak purplish red; luster metallic to adamantine; translucent on thin edges.

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Pyrargyrite, the sulphide of silver and antimony, is distinguished by its dark red color and the purplish streak. It may look like prousite, but is easily distinguished from the latter which has a scarlet streak. It also at times looks like hematite and cinnabar, but the hematite has a hardness of 6, and the latter has the bright red color throughout, while pyrargyrite turns black when exposed to the light, so that the characteristic red color will be seen only on fresh surfaces. The characteristic red color can only be kept on the mineral if it is constantly protected from the light.

Sometimes pyrargyrite occurs in crystals and these belong to the hexagonal system, and are prisms with low faces on the ends, as on plate 7, and the mineral is peculiar in that the faces on the opposite ends are unlike.

Pyrargyrite is found mostly in fissures and veins of quartz, fluorite, calcite, etc., and associated with pyrite, chalcopyrite, galena, etc. It is fairly common in Colorado in Gunnison and Ouray counties, in Nevada, New Mexico, Arizona, etc.

Prousite Ag₃ AsS₃ Pl. 7 light red silver

Usually occurs in irregular masses; hardness 2.5; specific gravity 5.6; color scarlet to vermilion; streak the same; luster adamantine; transparent on thin edges.

In general this mineral is very like pyrargyrite, but has the scarlet color and streak which are entirely characteristic. It is likely to have the surface tarnished black, which happens on exposure 37 to light, so that it is essential to be sure that fresh surfaces are being examined. Occasionally it is found in crystals, of the same type as the preceding mineral. It is generally found associated with pyrargyrite.

Cerargyrite AgCl horn silver

Usually found in irregular masses or incrustations; hardness 1 to 1½; specific gravity 5.5; color pearly gray, grayish green to colorless, but turning violet brown on exposure to light; luster resinous; transparent on thin edges.

This mineral is usually found in thin seams or waxy incrustations, but it may occur in crystals in which case they are cubes. It is very soft and easily cut with a knife, which with its tendency to turn violet-brown on exposure to light, makes it easy to identify. Cerargyrite is a secondary mineral, resulting from the action of chlorine-bearing water on some one of the sulphides of silver. It is found in the upper portions of mines, especially those in arid regions.

The Copper Group

After gold the next metal to be utilized was copper. About 4000 B.C. our early forefathers found that by heating certain rocks, they obtained a metal which could be pounded, ground and carved into useful shapes. Curiously enough the rocks which had the copper also had some tin in them, so that this first-found copper was not pure, but had from five to ten per cent of tin in it, making the resulting metal harder, and 38 what we call bronze. It was some thousands of years later before they distinguished the copper as a pure metal, but it worked and made good tools. The newly found metal was not as ornamental as gold; but, because it could be made into tools, it had a tremendous influence on man’s development. As the bronze tools began to take the place of the stone implements, the “Age of Bronze” was ushered in. In America the Indians in the Lake Superior region found native copper weathered out of the rocks and later mined it, and they too pounded it into knives, axes, needles, and ornaments, but probably never learned to melt it and mold their tools. At any rate they were not as far advanced in using this metal when Columbus landed as were the southern Europeans 6500 years earlier. Since the use of iron became general, copper has not held such a dominant place, but it still is “the red metal” which holds the second most important place.

It is malleable and ductile, though not equal to gold or silver in these respects. It is a good conductor of electricity and a very large amount of copper is used in electrical manufacture, roofing, wire, etc. It alloys with other metals; ten parts copper and one of tin being bronze, ten of copper and one of zinc is brass, and copper with aluminum is aluminum bronze.

Like silver and gold, copper is widely diffused through the igneous rocks, but before it is available, it must be leached out by solvents and concentrated in veins, fissures, or definite parts of the lavas or granites. The primary ores are 39 those which, while the igneous rock was still hot, were carried by hot vapors and liquids into the fissures and there deposited, mostly as sulphides. There is a long list of these, but in this country, the following are the commoner ones; chalcocite the sulphide of copper, chalcopyrite the sulphide of copper and iron, bornite another combination of copper, iron and sulphur, and tetrahedrite copper and antimony sulphide. When these primary ores are near enough to the surface to come in contact with waters carrying oxygen, carbon dioxide or silica in solution, they may give up their sulphur and take some one of these new elements and we have such forms as cuprite, the oxide of copper, malachite and azurite, carbonates of copper, or chrysocolla, the silicate of copper. Native copper is also a secondary deposit laid down in its present state by a combination of circumstances which deprived it of its original sulphur. In general copper mining can not be profitably carried on for ores with anything less than a half of one percent in them; and the use of such low grade ores has only been possible for a few years, as the result of inventing most delicate processes in the smelting.

The United States produces about a quarter of the world’s supply of copper, with Chile ranking second with about 17%.

Copper Cu Pl. 8

Usually in irregular masses; hardness 2.5; specific gravity 8.9; color copper red; luster metallic; opaque. Native copper, easily determined by its color 40 and hardness, is generally found in irregular grains, sheets, or masses, on which may sometimes be detected traces of a cube or an octahedral face, showing that it belongs to the isometric system. The most famous locality is the Upper Peninsula of Michigan which may be taken as typical. Here, long before it was known historically, the Indians found and dug out copper to make knives, awls, and ornaments.

In this region, beds of lava alternate with sandstones and conglomerates. The copper was originally in the lavas, but has been dissolved out, and now fills cracks and gas cavities in the lavas, and also the spaces between the pebbles of the conglomerate. This locality has been very famous both because of the quantity mined, and also because of the strikingly large masses sometimes found. Today but little of the ore runs above 2 percent copper, and it is mined if it has as little as ½ of one percent.

While nowhere near as abundant, native copper occurs in the same way in cavities and cracks in the trap rocks of New Jersey, and along the south shore of the Bay of Fundy. It is also known from Oregon, the White River region of Alaska, and in Arctic Canada.

Chalcopyrite CuFeS₂ Pl. 8 copper pyrites or yellow copper ore

Occurs in crystals of irregular masses; hardness 4; specific gravity 4.2; color bronze yellow; streak greenish black; luster metallic; opaque on thin edges.

Chalcopyrite resembles pyrite, but its color is a more golden yellow, and its surface 41 tarnishes with iridescent colors. Then too the hardness of chalcopyrite is but 4 as compared with 6 for pyrite. When in crystals this mineral belongs to the tetrahedral system as the c axis is but .985 in length as compared with I for the two other axes. This difference is so little that, to the eye, the octahedron appears to belong to the isometric system. Chalcopyrite occurs in octahedrons and tetrahedrons (as on plate 8), the latter being the form where but half of the octahedral faces are developed. However by far the most frequent mode of occurrence is in irregular masses.

This is the most important primary ore of copper, and is widely distributed, being found either in lavas, or in veins, or in fissures connected with igneous rocks. Apparently the deposits were made, either at the time of eruptive disturbances or shortly afterward, from vapors or hot solutions carrying the copper sulphides (and other sulphides) from the molten igneous rocks. Chalcopyrite is usually associated with pyrite, galena, sphalerite and chalcocite, as well as quartz, fluorite and calcite. It is found in all the New England States, in New York, New Jersey, Pennsylvania, Maryland, Virginia, North Carolina, Tennessee, Missouri, and all the Rocky Mountain and Pacific Coast States.

Bornite Cu₃FeS₃ purple copper ore

Occurs in granular or compact masses; hardness 3; specific gravity, 5; color bronze-brown with a bluish tarnish; streak gray-black; luster metallic; opaque on thin edges.

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Bornite is also known as erubescite, blushing ore, variegated copper, peacock copper, etc., all of which names refer to the highly iridescent tarnish which fresh faces soon take on when exposed to the air. Though usually in masses, it is sometimes found in rough cubes of the isometric system. In this country it is not abundant enough to be used as an ore, but is likely to be found with other ores like chalcopyrite or chalcocite. In the east it has been found at Bristol, Conn., and near Wilkesbarre, Penn., while in the west it may be expected to occur wherever other sulphide minerals of copper are found.

Chalcocite Cu₂S Pl. 9 copper glance

Occurs in fine grained compact masses; hardness 2.5; specific gravity 5.7; color dark leaden gray; streak black; luster metallic; opaque on thin edges.

Chalcocite is one of the important ores of copper, especially in Arizona and the Butte District of Montana. It resembles argentite in color and general appearance, but is readily distinguished by being brittle and having a tendency to tarnish to bluish or greenish colors on fresh surfaces. Occasionally it occurs in crystals which are in the orthorhombic system; but the edges of the prism are so beveled that there are six sides and the prism resembles a hexagonal prism (see page 16).

In the Butte, Mont., district, the most important copper region in the United States, fully 50% of the ore is chalcocite, which is a derivative of the originally deposited chalcopyrite, the latter 43 having lost its iron. In the veins of this district chalcopyrite, bournite, tetrahedrite, and several other copper minerals not described in this book, occur all together, and with them also gold, silver and arsenic minerals. The gold amounts to about 2¼ cents per pound of copper, and the silver is in somewhat less quantity. These veins were first opened to get the silver ores, which were the more important ones down to a depth of 200 to 400 feet. Below these depths the copper became much more important. It was the weathering which had removed a large part of the copper minerals in the upper levels of the veins, but had left a large part of the silver. Chalcocite is also important in most of the Utah and Arizona mines.

In the east it has been found at Bristol, Simsbury and Cheshire, Conn., and in the west it is found in all the Cordilleran States.

Tetrahedrite Cu₃SbS₃ Pl. 9 & 10 gray copper ore

Occurs in irregular masses and in tetrahedrons of the isometric system; hardness 3.5; specific gravity 4.7; streak dark brown; luster metallic; opaque on thin edges.

In its crystalline form the tetrahedrite occurs in tetrahedrons, which generally have faces formed by beveling the edges and by cutting the corners, as in the two figures of plate 10. Chalcopyrite may also occur in tetrahedrons, but its golden yellow color is entirely different from the gray-black of the tetrahedrite. When in masses the hardness and the streak which is dark brown, are very characteristic.

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In England and Bolivia tetrahedrite is an important ore of copper, but in this country it is simply a copper mineral which is widely distributed, and associated with most of the mining enterprises, but is in no case the important ore. It has been found sparingly through the New England States, at the Kellogg Mines in Arkansas, and abundantly in Colorado, Montana, Utah, Arizona, Nevada and New Mexico.

Cuprite Cu₂O Pl. 9 & 10 red copper ore

Occurs in isometric cubes, octahedrons, and dodecahedrons, or in masses; hardness 3.5; specific gravity 6; color dark brownish-red; streak brownish-red; luster metallic; translucent on thin edges.

When in crystals cuprite is easily determined, but when in masses its fresh surfaces may suggest prousite, but the streak and hardness are quite different in the two cases. Sometimes its color suggests hematite, but the latter has the hardness of 6. When found it is often coated with a thin film of green, which is malachite.

Except when found as native copper, the ore which contains the greatest percentage of copper is cuprite with 88.8% of copper. It is likely to occur in any of the deposits of copper ore, where they are in arid climates and above the level of the underground water, and is very frequently associated with malachite and azurite. In the Bisbee, Arizona, district cuprite is one of the important ores.

Besides the normal occurrence described above, cuprite may be found in two other varieties; 45 one where the crystals have grown side by side and so only the ends have been free for continuous additions of the mineral, which has resulted in a fibrous mass known as “plush copper ore” or chalcotrichite; the other an earthy mixture of limonite and cuprite, which is brick red in color, and termed “tile ore.”

Cuprite is found sparingly in New England, more abundantly at such places as Summerville and Flemington, N. J., Cornwall, Penn., in the Lake Superior region, and fairly abundantly in the Cordilleran States.

Malachite CuCO₃·Cu(OH)₂ Pl. 11

Usually occurs in nodular or incrusting masses; hardness 3.5; specific gravity 4; color green; streak a lighter green; luster adamantine, silky or dull; translucent on thin edges.

The vivid green of malachite is usually enough to determine it at once, but one may be sure by trying a drop of acid on it, in which case it effervesces as is characteristic of so many carbonates, but this is the only carbonate which is vivid green. Generally the malachite is in irregular masses, but crystals are occasionally found. These are extremely small and needle-like, and belong to the monoclinic system. In the Ural Mountains there is a locality where these crystals grow in fibrous masses, usually radiating from the center. Malachite in such nodules has a silky luster. These rare nodules have furnished the rulers of Russia with a unique and much prized material for making royal gifts. In European museums and palaces one finds 46 many objects carved from this form of malachite, and marked as gifts of the czars of Russia.

In the United States malachite is widely distributed, appearing as green streaks and stains where copper minerals have been exposed to the air. It is the green tarnish which appears on bronze and copper when exposed to the weather. It is found in large quantities in New Jersey, Pennsylvania, Wisconsin, Nevada, Arizona, Utah, New Mexico, etc. The Bisbee mine in Arizona is the place that has furnished museums with so many of the handsome specimens of malachite associated with azurite. These are the most striking specimens for the vividness of their colors that appear in any collections.

Malachite has been known since about 4000 B.C., the Egyptians having mines where they obtained it between the Suez and Mt. Sinai. In those early days it was particularly a child’s charm, protecting the wearer from evil spirits. It is still used as a stone of lesser value in making some sorts of jewelry.

Azurite 2CuCO₃·Cu(OH)₂ Pl. 11

Occurs as short prismatic or tabular crystals of the monoclinic system; hardness 4; specific gravity 3.8; color azure blue; streak lighter blue; luster vitreous; translucent on thin edges.

Azurite is another very striking mineral fully characterized by its color and streak. Like malachite it effervesces in acid. It is very near to malachite in composition, and by increasing its water content, can and freely does change to the green mineral; so that few specimens of 47 azurite are without traces of malachite. It is found in the same places as malachite, but is not as abundant in the east.

Azurite with the accompanying malachite is cut and polished to make semi-precious stones for some forms of jewelry.

Chrysocolla CuSiO₃·2H₂O

Never occurs in crystals, but in seams and incrustations; hardness 2-4; specific gravity 2.1; color bluish-green; streak white; luster vitreous; translucent on thin edges.

This rather rare mineral often appears in opal- or enamel-like incrustations, and its color is variable ranging from the typical bluish-green to sky-blue or even turquoise blue. This is a mineral resulting from the action of silica bearing waters, coming in contact with most any of the copper minerals, and is found accompanying cuprite, malachite, azurite, etc. It is never in large enough quantities to be used as an ore, but its striking color attracts attention and it can be found fairly frequently, especially in the west.

The Iron Group

Pure iron is a chemical curiosity which looks very much like silver. As obtained from its ores, or as it occurs in Nature, iron always has some impurities with it, such as carbon, silicon, sulphur and phosphorus, and these are highest in the crudest iron such as “pig-iron.” Its malleability and ductility are only a little less than for gold and silver, and so it has a wide range of qualities for use by man. It is only rarely found native in minute grains in some of the dark lavas. There 48 is however one remarkable exception to this statement, in that on Disco Island, Greenland, there is a basaltic rock, from which are weathered great boulders of native iron up to 20 tons in weight. This iron is very like that occurring in meteorites, and probably came from great depths in the earth’s interior. The specific gravity of iron is 7.8. It makes up around 5% of the crust of the earth, and probably occurs in much larger percentages in the interior of the earth.

Iron was discovered by man later than gold or silver or copper, about 1000 B.C.; but once found it was so much more abundant than any of these that it soon dominated over copper, and from Roman times to the present has been the basis of progress in civilization, and these times are well called “the iron age.”

Iron unites freely with the non-metals, and occurs as sulphides, oxides, carbonates, etc., and is also present as a secondary metal in that great group of minerals known as the silicates (see page 97). It alloys with a wide range of other metals, every combination altering the properties of the iron, and thus making it useful in a still greater range of manufacture. The introduction of ¼ to 2½% of carbon into iron makes steel, which is harder (in proportion to the amount of carbon) and stronger than the pure iron.

Iron compounds are among the most numerous and important of the colors in Nature’s paint box, limonite furnishing the browns which color the soil and so many of the rocks, hematite giving the red color to other abundant rocks, and magnetite often coloring igneous rocks black, 49 while the chlorophyll which gives the green color to plants is an iron compound, as is also the hemoglobin which gives the red to our blood.

Iron is present in all igneous rocks, and secondarily in the sedimentary and metamorphic rocks. It is soluble in water, and so is being constantly transferred from place to place, and changes from one compound to another, according to the circumstances in which it is placed.

The primary forms are pyrite, magnetite and the silicates. When in weathered rocks the iron is changed to limonite, siderite or hydrated silicates. Hematite is an intermediate oxide from which the water contained in limonite has been driven off by moderate heat or bacterial action.

Limonite 2Fe₂O₃·3H₂O Pl. 12

Never crystalline, occurs in mammillary, botryoidal and stalactitic forms, or in fibrous, compact, oolitic, nodular or earthly masses; hardness 5.5; specific gravity 3.8; color yellow-brown to black; streak yellow-brown; luster metallic to dull; opaque.

Limonite is a very common mineral, the color, streak and hardness identifying it readily. Iron rust is its most familiar form. When powdered it is the ochre yellow used in paints. Being so universally distributed, it is to be expected it will occur in a variety of ways. First, there is the fibrous type found lining cavities, in geodes, or hanging in stalactites in caves. This has a silky luster, an opalescent, glazed or black surface, and is in mammillated or botryoidal masses. Second, it may occur in compact masses in veins, where it was deposited by waters; which, circulating 50 through the adjacent rocks, gathered it from the rocks, and, on reaching the open seams, gave it up again. Third, it may occur in beds on the bottom of ponds, where it was deposited by waters which gathered it as they flowed over the surface of the country rocks. Measurements in Sweden show that it may accumulate in such places as much as six inches in the course of twenty years. In ponds and swamps, the decaying vegetation forms organic compounds, which cause the precipitation of the iron from the water, as it is brought in by the streams. This sort of iron in the bottom of ponds or swamps is also known as “bog iron.” Another form in which limonite may occur in ponds, lakes, or even the sea, is in oolitic masses. In this case the iron forms in tiny balls, with perhaps a grain of sand at the center, and one coat of iron after another formed around it, like the layers of an onion. If the resulting balls are tiny this is called oolitic (like fish eggs), but if the balls are larger it is pisolitic (like peas). Bacteria probably have a good deal to do with the precipitation of limonite in this manner. Fourth, limonite occurs in earthy masses, usually mixed with impurities like clay and sand, which are the residue left behind, where limestones have been dissolved by weathering. The fifth mode of occurrence is known as gossan, or “the iron hat,” which is a mass of limonite capping a vein of some sulphide mineral, like pyrite, chalcopyrite or pyrrhotite, which has been exposed to weathering; and in these minerals the sulphur has been removed, leaving a mass of limonite over the vein. This is 51 particularly common in the west. Limonite is quite easily fusible and so was probably the first ore from which early man extracted iron.

Limonite is iron oxide, with 3 molecules of water of crystallization (or constitution) associated with every 2 molecules of the oxide. If limonite is moderately heated the water is driven out and the resulting compound is hematite, the same oxide, but without the water. In this case and many other similar cases, as gypsum, opal, etc., we have two or more minerals resulting from the presence or absence of water in the mineral. The water molecules have a definite place in the arrangement of molecules which determines the structure of the mineral. Sometimes the water is driven out at a temperature around 212 F., in which case it is called, water of crystallization, but in other cases as gypsum, a considerably higher temperature is required to drive out the water, and then it is called, water of constitution. In all cases the removal of the water changes the arrangement of molecules and a new mineral results, with characteristics of its own.

In this case limonite is only one of a series of minerals which have the Fe₂O₃ molecule as a basis, and that incorporate more or less water into their molecular construction as follows:

Turgite 2Fe₂O₃·H₂O

Goethite Fe₂O₃·H₂O

Limonite 2Fe₂O₃·3H₂O

Xanthosiderite Fe₂O₃·2H₂O

Limonite Fe₂O₃·3H₂O

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Of these goethite is crystalline, the others non-crystalline. They may occur pure or in all sorts of mixtures, the mixtures usually being lumped under limonite. The limonite is far the commonest of the series, goethite is fairly common, but the others are rare as pure minerals.

Limonite is found in all parts of all states and in every country. Though so common, it is by no means an important source of iron today, only about one percent of the iron mined in this country coming from this source, though in Germany, Sweden and Scotland it is relatively much more important.

Goethite Fe₂O₃·H₂O Pl. 12

Occurs in lustrous brown to black orthorhombic prisms, usually terminated by low pyramids; hardness 5; specific gravity 4; color brown to black; streak brownish-yellow; luster imperfect adamantine; opaque.

Goethite, named for the poet Goethe, who was interested in mineralogy, is much less abundant than limonite or hematite, but occurs with them, when they are in veins. Its usual form is an orthorhombic prism with the edges beveled, and a low pyramid on either end. The crystals usually grow in clusters, making a fibrous mass, often radiated, in which case it is known as “needle iron stone”; or the prisms may be so short as to be almost scales; when, because of the yellowish-red color, it is called “ruby mica”. It is found in many states, including Connecticut, Michigan, Colorado, etc.

53

Hematite Fe₂O₃ Pl. 13 & 14 specular iron

Occurs in compact, mammillary, botryoidal, or stalactitic masses of dark red to black color, or in earthy masses of bright to dark red; hardness 6; specific gravity 5.2; color ochre red to black; streak cherry red to dark red; luster metallic, vitreous, or dull; opaque on thin edges.

Hematite is readily distinguished from other red minerals by its hardness and streak. It may occur in crystals, which belong to the hexagonal system, and are usually hemihedral forms of the double pyramid, or rhombohedrons. These rhombohedrons usually have the edges beveled, as in Pl. 13, A; or are tabular in form as a result of the beveling of two of the opposite edges to such an extent that a form like Pl. 13 B results. However the usual occurrence is in non-crystalline masses, which represent transformations from limonite by the loss of water of crystallization on the part of the limonite. In such cases we have fibrous, oolitic or compact masses, according to the form in which the limonite occurred. The transformation from limonite into hematite involves some heat to drive out the water of crystallization, but nothing like what is involved in metamorphism.

Hematite is the source of 90% of the iron mined in this country. Part of it comes from the famous Clinton iron ore, a layer a foot or more in thickness; starting in New York State, and extending all down the Appalachian Mountains to Alabama, where it is ten or more feet thick and the basis of the Birmingham iron industries. Then there are tremendous deposits 54 of earthy to compact hematite, probably derived from limonite, around the west end of Lake Superior. This latter region yields today around 75% of the iron for this country.

Loose earthy masses of hematite are often known as “ochre red,” and were used by the Indians for war paint. Today the same sort of material is obtained by powdering hematite and using it for red paint. The red color in great stretches of rock is due to the presence of small amounts of hematite, acting as cementing material. The red of the ruby, garnet, spinel, and the pink of feldspars and calcite are due to traces of hematite.

This mineral is very common and found in every state.

Magnetite Fe₃O₄ Pl. 14 Magnetic iron ore

Occurs in masses or in isometric octahedrons or dodecahedrons; hardness 6; specific gravity 5.8; color black; streak black; luster metallic; opaque on thin edges.

Magnetite is another important ore of iron, and is peculiar in being strongly magnetic; its name being derived, according to Pliny, from that of the shepherd Magnes, who found his iron pointed staff attracted by the mineral when he was wandering on Mount Ida. This magnetic property has been repeatedly used to locate beds of magnetite, and is very helpful in separating magnetite from the “black sands,” of which it so often forms a part. These sands however generally have magnetite with so much titanium in it that they are unfit for smelting.

55

Magnetite is found in association with igneous or metamorphic rocks, and often represents limonite or hematite which has been altered as the result of high temperatures. Some of it, in the igneous rocks especially, was undoubtedly in the molten magma and has crystallized out from the magma while it was still hot. It is the form of iron always indicative of former high temperatures. It is an ore mineral for about 3% of the iron in this country, but in Scandinavia and some other countries, it plays a leading role as the source of iron.

It is found in the Adirondack Mountains, in New Jersey, Pennsylvania, Arkansas, North Carolina, New Mexico, and California.

Siderite FeCO₃ Pl. 13 & 14 Spathic iron

Occurs in fibrous botryoidal masses or rhombohedral crystals, sometimes with curved faces; hardness 3.5; specific gravity 3.8; color gray-brown; streak white; luster vitreous; translucent on thin edges.

Like hematite this mineral belongs to the hexagonal system, and crystallizes in hemihedral form, making the rhombohedron. Its faces are often curved, which is rare in minerals, only a few forms like this and dolomite having other than plane faces. When siderite crystals grow in clusters, the crowding often results in growth on one face only, making a mass of fibrous character, and in such cases the surface of the mass is botryoidal in contour. The mineral is likely to oxidize, losing its gray-brown color, and becoming limonite. In the United 56 States it is scarcely ever used as an ore for iron, but in Germany and England a great deal of iron is smelted from this mineral.

It occurs in Massachusetts, Connecticut, New York, throughout the Appalachian Mountains, and also in Ohio.

Pyrite FeS₂ Pl. 15 & 16 iron pyrites

Occurs as cubes, octahedrons and pyritohedrons, or in compact masses, scales or grains; hardness 6; specific gravity 5.1; color brassy yellow; streak greenish-black; luster metallic; opaque on thin edges.

This is one of the commonest of all minerals. It is found in all kinds of rocks, with all kinds of associations, in all parts of the world. Its crystals are isometric, and cubes and octahedrons are abundant. The pyritohedron is also a common form, and characteristic of this mineral. It is a hemihedral form derived from a 24-sided form, i.e. the cube with four faces on each side. On this 24-sided form each alternate face has developed and the others have disappeared, resulting in a 12-sided form, known as the pyritohedron, which differs from the dodecahedron in that each of its faces is five-sided instead of rhomboidal. When in crystals pyrite can not be easily confused with any other mineral; but when in masses it is often mistaken for gold, chalcopyrite, pyrrhotite or marcasite. From the first two, the color should be sufficient to distinguish it, for they are golden yellow. Pyrrhotite is bronze yellow, and marcasite is paler yellow. Then too in hardness pyrite is 57 much harder than any of these minerals except marcasite. This last is the one which is most likely to cause real difficulty. Its lighter color, and the fact that it usually comes in fibrous masses are the best distinctions.

In spite of being so abundant pyrite is scarcely ever used as an ore for iron, because the sulphur makes the metal “short,” or brittle, and the sulphur is not easily gotten entirely out of the iron; but pyrite is used largely in the manufacture of sulphuric acid, so important to many of our industries.

Other sulphides are commonly mixed with pyrite, such as chalcopyrite, arsenopyrite, argentite, etc.; but the most important impurity is gold, which is often scattered through the pyrite in invisible particles, and sometimes in quantities enough to make it worth while to smelt it for the gold.

Pyrite is particularly the form in which the sulphur compounds of iron appear in rocks which have been highly heated, and is to be expected in metamorphic rocks and also igneous rocks, especially in fissures and veins leading from the igneous rocks. It may occur in sedimentary rocks, but in these last it is usually marcasite.

Marcasite FeS₂ Pl. 15 white pyrite

Occurs in orthorhombic crystals, usually grouped to make fibrous or radiating masses, or non-crystalline in masses; hardness 6; specific gravity 4.8; color pale brassy-yellow; streak greenish-gray; luster metallic; opaque on thin edges.

Marcasite has the same chemical composition, 58 as pyrite, and looks like it, but is lighter colored and usually occurs in fibrous masses. It is the commoner form in limestones and shales, while pyrite is more likely to occur in igneous and metamorphic rocks. It seems probable that marcasite is due to a more hasty precipitation from cold solutions, while pyrite is deposited more slowly from hot solutions.

Isolated crystals of marcasite are rare; but, if formed, they belong to the orthorhombic system. Usually some form of twinning is present, and because of the multiple character of the twinning, marcasite crystals usually show a ragged outline, with reentrant angles. It is most abundant in radiated masses, which appear fibrous on the broken surfaces. It decomposes easily, taking oxygen from the air and forming, even in museum cases, a white efflorescence or “flower,” which is iron sulphate or melanterite. In moist air it takes water and decomposes to sulphuric acid which may change the surrounding limestone to gypsum. Marcasite is found wherever limestones and shales are the country rock.

Pyrrhotite Fe₁₁S₁₂ Magnetic pyrites

Occurs in masses; hardness 4; specific gravity 4.6; color bronze; streak grayish-black; luster metallic; opaque on thin edges.

Tabular crystals are known, but are very rare. They belong to the hexagonal system. This form is easily distinguished from the other yellow minerals by being magnetic. It is by no means as abundant as the two preceding sulphides of iron, but does occur fairly frequently in veins 59 in igneous rocks, and less frequently in limestones, large quantities of sulphuric acid being made from a deposit in limestone at Ducktown, Tenn. It will be found in most states. When associated with nickel it is an important source for the latter mineral, as at Sudbury, Canada. Pyrrhotite is very like a substance found in meteorites, known as troilite.

The Lead Group

After learning how to get iron from the rocks by rude smelting methods, the early peoples tried heating various rocks, and some time around 500 B.C. stumbled upon lead, which is rather easily separated from its ores. This metal was used through Roman times to make pipes, gutters, etc.

Lead is a soft metal, fairly malleable, but with little ductility, and still less tensile strength. Though one of the commoner metals, it does not occur as pure metal in Nature. It is diffused in minute quantities through the igneous rocks, and also is found in the sedimentary rocks and in the sea water. Its minerals are few, galena, the sulphide of lead, being the commonest, and at the same time the form in which lead is primarily deposited. Galena may also represent a secondary deposition. The other minerals, cerrusite, anglesite, and pyromorphite are results of modification of the galena when it lies near enough to the surface to be acted on by weathering agents, like water and air. Lead minerals are usually associated with zinc minerals, there being but few places where the minerals of the one group occur 60 without the other. Most lead when first smelted from its ore, contains a greater or less amount of silver in it, sometimes enough so that the lead ore is better worth working for the silver than for the lead.

Lead is used in making pipes, gutters, bullets, etc., and in its oxide forms in the manufacture of paints and glass. Eighty-three parts of lead with 17 parts of antimony make type metal. Lead and tin alloy to make solder. Lead and tin with small amounts of copper, zinc and antimony make pewter. The United States produce about 20% of the world’s supply of this metal.

Galena PbS Pl. 17 lead glance

Occurs in cubes or cleavable masses; hardness 2.5; specific gravity 7.5; color lead-gray; streak lead-gray; luster metallic; opaque.

While there is quite a group of lead-gray minerals, galena is easily identified by its cleavage, which is perfect in three directions parallel to the cube faces. Even a moderate blow of the hammer will shatter a mass of galena into small cubic pieces. The crystals often have the corners cut by octahedral faces, and occasionally the edges are beveled by dodecahedral faces. It is not uncommon to find crystals of large size, several inches across. If galena has 1 to 2% of bismuth as an impurity, curiously enough, the cleavage changes to octahedral, but this is a rare occurrence.

Galena may occur as a primary mineral in veins associated with igneous intrusions, or in irregular 61 masses in metamorphic rocks; but it is more often found in irregular masses in limestones, where the limestone has been dissolved, and the cavities thus formed, filled with secondary deposits of galena. It also occurs at the contact between igneous rocks and the adjacent rock, whatever this may be. Sometimes it is found in residual clays.

Among the most important lead deposits are the Cœur d’Alene district in Idaho, where galena with a high percentage of silver is mined; the Leadville, Colo., district where lead, silver and gold occur together in veins; the Joplin, Mo., district, where lead and zinc ores occur together in irregular masses in limestones; and the Wisconsin district of similar character.

When found galena is usually associated with sphalerite, argentite chalcopyrite, pyrite and calcite. It will be found in every state.

Cerrusite PbCO₃ Pl. 18 White lead ore

Occurs in fibrous or compact masses, or in orthorhombic crystals, usually on galena; hardness 3.5; specific gravity 6.5; colorless; streak white; luster adamantine; transparent on thin edges.

While the crystals of this mineral simulate hexagonal, they are actually orthorhombic, the simple form being an octahedron with two of its edges beveled, making double six-sided pyramids (see Pl. 18 A.) Usually prism faces are present. Twinning is common, both the simple contact sort, as shown on Plate 18 B, and also the sort in which three crystals have grown through each 62 other, so as to make a six-rayed crystal. The considerable weight, and the fact that it effervesces in acid serve to identify cerrusite. When pure it is colorless, but impurities cause it to appear white, gray or grayish-black, and sometimes it has a tinge of blue or green.

It is likely to occur wherever galena is found, as a secondary mineral derived from the galena. In this country it is not used as an ore, for, as in the Leadville district, veins which have cerrusite near the surface change at moderate depths, and galena takes the place of the cerrusite. It is found all down the Appalachian Mountains, and in all the Cordilleran States. Especially fine specimens have come from the Cœur d’Alene district in Idaho.

Anglesite PbSO₄ Pl. 18

Occurs in grains and masses, or in tabular and prismatic orthorhombic crystals; hardness 3; specific gravity 6.3; colorless; luster adamantine; transparent on thin edges.

Two modes of occurrence are characteristic, one in cavities in galena, the other in concentric layers around a nucleus of galena. In the former case fine crystals are developed, in the latter the mineral is in masses. The crystals look like those of barite, but are soluble in nitric acid while the barite is insoluble. Sometimes the crystals are prismatic with pyramidal faces instead of the tabular form.

It is found in the lead mines associated with galena, and in this country is not used as an ore for lead, but in Mexico and Australia it is 63 abundant enough to be mined as an ore. Exposed to water which has carbon dioxide in it, and most surface waters have some, it readily changes to cerrusite. It is found in Missouri, Wisconsin, Kansas, Colorado, and Mexico.

Pyromorphite Pb₅Cl(PO₄)₃ Pl. 17 Green lead ore

Occurs in small barrel-shaped hexagonal crystals, and in fibrous or earthly masses; hardness 3.5; specific gravity 7; color green to brown; luster resinous; translucent on thin edges.

Pyromorphite is found in the upper levels of lead mines, and is formed by the decomposition of galena. Its green color (sometimes shading off toward brown), considerable weight and resinous luster, serve to distinguish this mineral. The crystal form is that of a simple hexagonal prism, with the ends truncated. It is found in Phœnixville, Penn., Missouri, Wisconsin, Colorado, New Mexico, etc.

The Zinc Group

Zinc and copper made the brass of early Roman times; but even then, zinc was not known as a separate metal, the brass being made by smelting rocks in which both zinc and copper occurred, the zinc never being isolated until much later. Some time in the later Roman times it seems to have been obtained separately, but then and all down through the Middle Ages zinc and bismuth were confused. Our earliest record of zinc being smelted, as we know it today, was about 1730 in England. In those earlier 64 days, the product, zinc, or bismuth, or both together, were known as “spelter,” and this name has clung to zinc in mining and commercial circles; so that today, if one looks for quotations in the newspaper, he often finds zinc under the head of spelter.

Zinc, like lead, is diffused in small quantities through all the igneous rocks. In places it is segregated in fissures or veins leading from the igneous rocks, along the contact between igneous rocks and either sedimentary or metamorphic rocks, in limestones where solution cavities have been formed and later filled with zinc minerals, and as a residue where limestones have been weathered away. In all these places it is closely associated with lead.

The sulphide, sphalerite, is the primary mineral, and the other minerals, like zincite, smithsonite, calamine, willemite, franklinite, etc., are secondary, resulting from modifications of the original sphalerite. In connection with zinc minerals the region of Franklin Furnace, N. J., is especially interesting, for at that place are found two large metamorphosed deposits containing a wide range of zinc minerals, several of which are not found anywhere else.

Zinc is soft and malleable, but is only slightly ductile, and has little tensile strength. It alloys with several metals, and in this form is most useful today; three parts of copper to one of zinc making brass; four or more parts of copper and one of zinc, making “gold foil”; copper and zinc (a little more zinc than copper) making “white metal”; three parts of copper to one of 65 zinc and one of nickel making German silver; etc. Zinc is also used in large quantities in galvanizing iron, sheets of iron being dipped into melted zinc and thus thinly coated. It is also used in batteries and a wide range of chemical industries.

Sphalerite ZnS Pl. 19 & 20 zinc blende, black jack

Occurs in grains, in fibrous or layered masses, or in isometric crystals; hardness 3.5; specific gravity 4; color yellow-brown to almost black; streak light yellow to brownish; luster resinous to adamantine; translucent on thin edges.

When in crystals sphalerite occurs most commonly either in dodecahedrons or in tetrahedrons (hemihedral forms of the isometric octahedron). The cleavage is fairly good and parallel to the faces of the dodecahedron. The difficulty usually is to get large enough crystalline masses to see this cleavage clearly, but by examining the angles between the faces of cleavage pieces they will be found to be the same as those on a dodecahedron. When the mineral is pure, it has the color of resin, but sometimes it is reddish to red-brown, and then it is called “ruby zinc,” more often it is dark brown due to the presence of iron as an impurity. This is what the miners call “black-jack.” The presence of iron also tends to make the streak darker. The hardness, streak and cleavage will usually determine this mineral readily.

Sphalerite is the primary ore of zinc and is usually found in fissures and veins leading from 66 masses of igneous rocks, or along the surface of contact where igneous rocks like granite or lavas come against such metamorphic rocks as gneisses, schists, or crystalline limestones. In the region of Joplin, Mo., however, the sphalerite is of secondary character, having been gathered by waters circulating through the limestones, and deposited in them in irregular pockets. This Joplin district has produced more zinc than any other in the world. The United States annually produces about 25% of the world’s supply of this metal.

Sphalerite is always associated with galena, and such other minerals as argentite, pyrite, chalcopyrite, fluorite, quartz, calcite and barite, are very apt to be present. It will be found in almost every state, especially in fissures and veins, and less frequently in cavities in limestones.

Zincite ZnO Pl. 19 & 20 red zinc ore

Usually occurs massive, but may be found in crystals; hardness 4; specific gravity 5.6; color deep red; streak orange; luster subadamantine; translucent on thin edges.

When in crystals zincite forms in hexagonal prisms with hexagonal pyramids on the ends. This is rather rare, most of the zincite being found in massive form. The cleavage is parallel to the prism faces and perfect. The deep red color and orange streak are wholly characteristic.

This mineral is so common at Franklin Furnace, N. J., as to be an important ore, but it is very seldom found elsewhere. This district, as 67 mentioned before, is a peculiar one for zinc minerals. The zinc beds are in a metamorphosed limestone, and into this are intruded numerous dikes of granite. Probably the zinc was originally present in the bed of limestone as smithsonite, calamine and other secondary minerals of zinc. When intruded by the hot granite the smithsonite (carbonate) may well have been altered to the oxide, zincite; while the calamine (hydrous silicate) became the simple silicate, willemite.

Willemite ZnSiO₄ Pl. 20

Occurs in masses or in crystals; hardness 5.5; specific gravity 4.1; color pale yellow when pure; luster resinous; translucent on thin edges.

Willemite is another of the minerals which are distinctively characteristic of Franklin Furnace, and found elsewhere very rarely. It is so common there as to be one of the principal ores, and mostly occurs in irregular masses, but is also found in crystals. These are hexagonal prisms, with a three-sided (rhombohedral) pyramid on the ends. The color when pure is whitish or greenish-yellow, but with small amounts of impurities it may be flesh-red, grayish-white or yellowish-brown. When in crystals it is easily determined; but when massive it looks like calamine, and can only be distinguished by placing a bit of the mineral in a closed tube and heating it, in which case calamine will give off water vapor, while willemite will not.

This mineral is one of those resulting from metamorphic alteration and is derived from 68 calamine, when the latter loses its water of crystallization. It is common at Franklin Furnace, N. J., and also found occasionally elsewhere, as at Salida, Colo., and in Socorro Co., New Mexico.

Calamine Zn₂(OH)₂·SiO₃

Occurs as crystalline linings in cavities, or as botryoidal or stalactitic masses; hardness 5; specific gravity 3.4; colorless to white; luster vitreous.

Calamine resembles both smithsonite and willemite when in non-crystalline masses. From the smithsonite it is easily separated by the fact that in nitric acid the smithsonite effervesces and the calamine does not. From willemite it is harder to distinguish, but a piece may be placed in a closed tube and heated. If it is calamine water vapor will be given off, if willemite nothing happens. When calamine occurs in crystals these are orthorhombic and mostly tabular, and the crystals are peculiar in that the two ends are terminated differently.

Both this and smithsonite are secondary minerals and usually occur together when zinc is found in limestones. It is abundant at Franklin Furnace and Sterling Hill, N. J., and also found at Phœnixville, Penn., in Wythe Co., Va., and Granby, Mo.

Smithsonite ZnCO₃ Pl. 21 Dry bone

Usually occurs as incrustations, grains, earthy or compact masses, and as crystals; hardness 5; specific gravity 4.4; color white, yellow, greenish or bluish; streak white; luster vitreous; transparent on thin edges.

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When pure this mineral is colorless, but, as it occurs, it is usually white, or tinged with some shade of yellow, green, or blue, but in all cases its streak is white. The crystals are rhombohedrons often with edges beveled or corners cut by other faces. It resembles calamine and willemite, but is readily separated from either of these by the acid test, for smithsonite effervesces when acid is placed on it.

Next to sphalerite, smithsonite is the commonest of the zinc minerals. It is a secondary mineral, resulting from the action of lime-charged water acting on sphalerite, and so is likely to be found wherever zinc minerals occur in a limestone region. In the Wisconsin-Illinois-Iowa district it serves as a minor ore of zinc, and is termed here “dry bone.” It is also found in the Missouri and Arkansas districts, and in Europe is an important ore for zinc.

Franklinite (ZnMn)Fe₂O₄ Pl. 21

Occurs in compact grains or masses, and in isometric octahedrons; hardness 6; specific gravity 5; color black; streak reddish-brown; luster metallic; opaque on thin edges.

This is a mineral peculiar to the Franklin Furnace region, from which it gets its name. It looks like magnetite, but its reddish-brown streak and lack of magnetism distinguish it. When it occurs in octahedrons, the edges are rounded, while those of magnetite are sharp. It is a complex and variable oxide of zinc, iron and manganese, which has resulted from the metamorphism of the beds in which it occurred 70 probably being originally something quite different.

The Manganese Group

Though manganese was known in the mineral pyrolusite in early times, it was then thought to be magnetite or magnetic iron ore. It was not until 1774 that it was isolated and recognized as a distinct element.

Manganese is one of the lesser elements in the crust of the earth, making less than .07 of one percent, but as an alloy with other metals, especially iron, it has attained a considerable importance to man. It is used chiefly with iron, 20% of manganese making the alloy, spiegeleisen, a combination which occurs in Nature in Germany, and from 20% to 80% making ferromanganese. These alloys are in great demand because they make an especially tough steel essential in the manufacture of munitions. The sources for manganese are the oxide ores, manganite, pyrolusite and psilomelane, which have been formed as secondary minerals, as a result of the weathering of silicates which carry manganese. They occur widely enough, but throughout the United States the deposits are small, and this is one of the elements in which this country is not self-sufficient. The largest producer of manganese is Russia; however she consumes almost all of her output at home, and our supply comes from the next largest producers, India, the Union of South Africa, and the Gold Coast. A shift in trade may be expected when Brazil’s recently discovered ore body in Matto Grosso is brought into full production. 71 Besides being used as an alloy, manganese is employed in making paints and dyes, for clearing glass, and for some types of electric batteries.

Pyrolusite MnO₂

Occurs in earthy or fibrous masses; hardness 1-2; specific gravity 4.8; color black; streak black; luster dull; opaque.

Pyrolusite occurs in soft masses and incrustations, usually leaving a sooty mark on the fingers. Sometimes it seems to be in crystals, but these are pseudomorphs which have the form of manganite, from which the pyrolusite has formed as a result of the water having been driven from the manganite. Frequently pyromorphite and manganite will be found together, and in some cases the outer part of a mass or crystal will be pyrolusite, while the center is still manganite. Psilomelane is another oxide of manganese with water and may appear very like pyrolusite, but both manganite and psilomelane have much greater hardness than does pyrolusite. If there is difficulty in deciding about pyrolusite, it may be placed in a closed tube and heated. It will not be affected by the heat, while, under the same circumstances, both manganite and psilomelane will give off water vapor.

Pyrolusite usually occurs in black streaks or pockets in residual clays which have formed as a result of the decomposition of limestones. It may also occur in dendritic forms in seams and crevices (see manganite). It is found in Vermont, Massachusetts, Virginia, Arkansas, Colorado, California, etc.

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Psilomelane MnO₂·H₂O

Occurs in compact botryoidal or stalactitic masses; hardness 5-6; specific gravity 4.2; color black; streak brownish-black; luster metallic; opaque on thin edges.

Psilomelane is very like pyrolusite, and often occurs with it. It is distinguished by its greater hardness, and the fact, that when heated in a closed tube, it gives off water vapor. From manganite it is more easily distinguished, for it never occurs in crystals, while the manganite is usually crystalline. This and pyrolusite are the principal ores of manganese.

Wad is an impure form of psilomelane, having some iron oxide mixed with the manganese oxide, usually limonite; or the impurity may take the form of a copper, cobalt, lithium or barium oxide.

Psilomelane is found at Brandon, Vt., in Arkansas, Colorado, California, etc.

Manganite Mn₂O₃·H₂O Pl. 22

Occurs in prismatic crystals, or in columnar or fibrous masses; hardness 4; specific gravity 4.4; color steel gray; streak reddish-black; luster submetallic; opaque on thin edges.

This is the form taken by manganese oxide when it crystallizes in the presence of moisture, and pyrolusite frequently changes to manganite when exposed to moisture. The crystals are orthorhombic prisms, with striated sides and the ends truncated. These prisms usually occur in bundles and give the mineral a fibrous appearance. Manganite is not hard to identify, the 73 striations on the crystals and the streak being very characteristic.

In seams and tiny crevices this mineral, and often pyrolusite, grows in a branching manner, resembling tree-like or “mossy” masses. This is termed dendritic, and the growths of manganese minerals are called dendrites. One of the most curious of these is when the “mossy” growth is inclosed in chalcedony, making the so-called moss agate. These moss agates are abundant through the Rocky Mountains and are frequently cut for semi-precious stones. The finest ones however come from India and China.

Manganite is found in the Lake Superior region, Colorado, etc.

Rhodochrosite MnCO₃

Occurs in compact cleavable masses; hardness 4; specific gravity 3.5; color rose to dark red; streak white; luster vitreous; translucent on thin edges.

This usually occurs in pink to red masses which cleave readily parallel to the faces of the rhombohedron. When it is found in crystals, which are rare, these too are rhombohedrons. It is usually found in veins as a gangue mineral with copper, silver or zinc ores. Its beautiful color and the fact that it effervesces in acid serve to distinguish this mineral. It is found at Branchville, Conn., at Franklin Furnace, N. J., and in veins with silver in Colorado, Nevada, and Montana.

The Aluminum Group

Though aluminum is one of the most abundant of all the metals, making some 8% of the crust of 74 the earth, its union with other elements is so firm, that only recently have methods been found for getting the metal free. It was first isolated in 1846, but up to 1890 the extraction of aluminum was so expensive, that it could not be widely used. About that time electrical processes were applied to its extraction, and since then the price has steadily dropped, until now it is under $.20 per pound. It is very malleable, and ductile, and has high tensile strength. Exposed to the air, water or ordinary gases, it does not tarnish; and it is very light, an equal bulk weighing about a third as much as iron. The combination of lightness and strength, and the fact that it is a good conductor of electricity, have made it available for a wide range of uses, such as electrical apparatus, delicate instruments, boats, aeroplanes, and domestic utensils.

It is an essential component of all the important rocks, except sandstone and limestone, and combines to a greater or less degree in a host of minerals. Though present in clays, shales, argillites, feldspars, and micas, it is only from bauxite that it has been successfully extracted. Aside from the small number of simple compounds of aluminum grouped here, it also takes a part in the make-up of a large series of minerals termed silicates, treated a little further on in this book.

It alloys with other metals, especially copper. The union of copper and a small amount of aluminum makes aluminum-bronze, which looks like gold and is used for watch chains, pencil-cases, etc., and also for the antifriction bearings 75 of heavy machinery. A small amount added to steel prevents air holes and cracks in casting.

Corundum Al₂O₃ Pl. 23

Occurs in cleavable masses or in hexagonal crystals; hardness 9; specific gravity 4; colorless, red, yellow, blue, or gray; luster vitreous to adamantine; translucent to transparent on thin edges.

Corundum is readily recognized by its hardness, second only to that of the diamond. The crystals may be simple six-sided prisms, hexagonal pyramids or combinations of the two. The cleavage is usually described as parting, for it is by no means perfect, but when it is recognizable it is parallel to the faces of a rhombohedron, and cleavage pieces may appear almost cubic.

When in clear and perfect crystals this mineral is one of the most highly prized of all the gems. Clear and colorless it is known as the “Oriental white sapphire”; when tinged with blue it is the sapphire; when colored yellow, the “Oriental topaz”; when green, the “Oriental emerald”; when purple, the “Oriental amethyst” and when red, the ruby. Sapphires range from colorless to deep blue, the value depending on the shade of the blue, and increasing as the color deepens. The Oriental topaz can easily be confused with the true topaz, which is a much commoner and less valuable gem, but can be distinguished by the hardness, topaz having a hardness of but 8. The name emerald is applied to several green gems, mostly to beryl, which is not so hard and is the true emerald. The Oriental emeralds have 76 a value about the same as diamonds. Rubies of clear and deep color are the rarest of all gems, ranging in value about three times as high as diamonds of equal size. The most sought-for shade is the so-called “pigeon-blood red,” and the value of a stone of this sort is almost dependent on the whim of the buyer. The best of the rubies come from granites or metamorphosed limestones in Burma; the best sapphires from Ceylon, though both of these, and some of the other corundums of gem quality, have been found in North Carolina and Montana.

Around these stones, which have been used so long among the Hindus, Persians, Jews, Egyptians, and Christians, a wealth of lore has been woven. The sapphire was Saturn’s stone, and a talisman to attract Divine favor. Where tradition makes the stone on which the ten commandments were written the sapphire, it is probable that, what was really meant, is lapis lazuli, as is also the case when sapphires are mentioned as building stones for the celestial gates. The ruby in ancient lore is termed “lord of stones,” “gem of gems” etc., and so protected its wearer that he was safe from injury in peace or war.

When corundum is colored brown by impurities of iron, it is termed corundum, when black by greater quantities of iron, it is emery. These varieties are far the commonest form in which corundum occurs, and when ground to finer or coarser powder make the commercial emery. Emery is likely to be found in sands, making so-called “black sands,” where it has accumulated as a result of the weathering to bits corundum-bearing 77 rocks. In some one of its forms, corundum is found in Massachusetts, Connecticut, New York, New Jersey, and all down the Appalachian Mountains, also in Colorado, Montana, California, etc.

Bauxite Al₂O₃·2H₂O

Occurs in grains, or oolitic or clay-like masses; hardness 1-3; specific gravity 2.5; color white to yellowish-white or reddish-brown.

Bauxite never comes in crystals, but is usually in earthy masses, which have resulted from the decomposition of granitic or volcanic rocks, in circumstances where hot alkaline waters were present. This explanation seems to apply especially to the deposits in France, which were first the chief source of the bauxite, and may be applicable to those in Georgia and Alabama. Some of the other deposits, however, do not seem to have had any hot water available, and the deposit appears more like simple decomposition of the underlying rocks by alkaline waters.

In many cases bauxite resembles limonite in being a mixture of two or more aluminum oxides with water of crystallization, such as Al₂O₃·H₂O, Al₂O₃·2H₂O and Al₂O₃·3H₂O. This is particularly true of the bauxite which resulted from the decomposition of rocks by surface water.

Bauxite is the ore from which aluminum is obtained. The deposits are not large, but the United States has its share of them. It is found in Alabama, Arkansas, Georgia, Missouri, Tennessee, and California.

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Cryolite Na₃AlF₆ Ice stone

Occurs in pseudo-cubic crystals or massive; hardness 2.5; specific gravity 3; color white; luster vitreous; transparent on thin edges.

Cryolite is a relatively soft mineral, colorless to white as snow; for which reason, and partly also because it comes mostly from Greenland it is called “ice stone.” It is really monoclinic but the inclination of the c axis is so slight, that, unless examined carefully, the crystals appear to be cubic. Until about 1900 great quantities of this mineral were shipped from West Greenland, and from them the metal aluminum was extracted. When bauxite was discovered, it was found to be considerably cheaper to make the aluminum from that mineral, and now cryolite is no longer sought. Aside from its occurrence in Greenland some cryolite is found in Colorado, near Pike’s Peak.

The Arsenic Group

The metal, arsenic, is a dark steel gray in color, when the surface is fresh, but it soon tarnishes. It is very brittle and easily powdered under the hammer, and its only use as a metal, is for an alloy with lead in making shot. Its compounds find a wider use. The white powder called “arsenic” is arsenous acid, and is used mostly in making poisons, which fortunately are easily detected in animal tissues. Copper arsenate, (Scheele’s green) is a pigment used in making green paint, and formerly in the green colors of wall paper. A combination of arsenous acid, copper oxide and acetic acid is the well 79 known Paris Green, so much used for an insecticide. Beside these uses, arsenic serves a large number of other purposes, as in making glass and enamel, embalming fluids, and various medicines.

Curiously arsenic plays a double part, acting part of the time as a metal, as in the two following minerals, and part of the time as a non-metal, as in cobaltite, niccolite, etc.

Arsenopyrite FeAsS Pl. 24

Occurs in well formed crystals, grains, or masses; hardness 5.5; specific gravity 6; color silver-white; streak black; luster metallic; opaque on thin edges.

When in crystals, they are usually short prisms of the orthorhombic system, either end being terminated with a low roof. Though usually described as silver-white in color, there is always a brassy cast to the color. Its appearance is much like cobaltite and smaltite, but it can be easily distinguished from both these by putting a piece in nitric acid. The arsenopyrite will not materially change the color of the fluid, but the other two turn it rose-red, and all give off the smell of sulphur. It looks sometimes like marcasite, but that is yellower, and has the fibrous structure, not found in arsenopyrite.

It is found in veins or in metamorphic rocks, associated with argentite, galena, sphalerite, chalcopyrite and pyrite. It is distinctly a mineral formed by deposition from hot vapors or hot water rising from either lavas, or in the course of metamorphism.

It is found in New Hampshire, Vermont, 80 Massachusetts, Connecticut, New York, New Jersey, California, etc.

Realgar AsS Pl. 24

Occurs in incrustations or scattered grains; hardness 1.5 to 2; specific gravity 3.5; color orange; streak orange; luster resinous; opaque on thin edges.

Crystals are very rare, but when found are short monoclinic prisms. The color is aurora-red, changing to orange as soon as it is exposed to the air. This and the streak are entirely characteristic. It is a mineral associated with hot vapors or hot waters, and is found about volcanoes, as deposits from the hot water of the geysers in Norris Basin, Yellowstone Park, and in veins, associated with barite, stibnite, quartz, etc., as in Massachusetts, Utah, California, etc.

Orpiment As₂S₃

Occurs as incrustations or powdery masses; hardness 1 to 2; specific gravity 3.5; color lemon yellow; streak yellow; luster resinous.

This mineral is very like realgar in its physical properties, and likely to occur with it. It gives the lemon yellow color to the basins about hot springs, as in the Yellowstone Park, and about volcanoes. It also comes in veins with realgar.

Molybdenum

Molybdenum is a rare metal, silvery-white in color, brittle and very difficult to fuse. It is used mostly as an alloy of steel, to make certain grades of tool steel. The world’s greatest supply is obtained from Climax, Colorado, where the principal ore mineral is molybdenite.

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Molybdenite MoS₂

Occurs in scales or scaly masses, occasionally in tabular hexagonal crystals; hardness 1.5; specific gravity 4.7; color lead-gray; streak bluish-gray; luster metallic; opaque.

This mineral is the chief source for the metal molybdenum. Its extreme softness and greasy feel will distinguish it at once from any other mineral except graphite, which has much the same qualities, but its scaly character and the more bluish tinge in streak and color will distinguish these two.

It occurs in granites, gneisses, and metamorphic rocks in Colorado, New Mexico, Maine, Connecticut, New Hampshire, New York, Pennsylvania, etc.

Antimony

Antimony is another hard, brittle metal, of bluish-white color. Exposed to the air at ordinary temperatures it does not tarnish; and this combined with its hardness make it useful for such alloys as Britannia metal, type metal, and pewter. Only one of its minerals, stibnite, is common enough for mention.

Stibnite Sb₂S₃ Pl. 25 gray antimony

Occurs in prismatic or needle-like crystals; hardness 2; specific gravity 4.5; color lead-gray; streak lead-gray; luster metallic; opaque.

The crystals of stibnite are orthorhombic and usually elongated, the sides striated and the ends with low pyramids 82 on them. Sometimes the long crystals are curved or even twisted. There is a well-developed cleavage parallel to face b in the figure. While the color is similar to that of galena, the form and cleavage are so different that stibnite is easily determined.

The ancients used stibnite to color their eyebrows, now it is the source for the metal antimony. Hungary and Japan are famous for the fine large crystals they produce; but moderate sized crystals may be found in this country. It occurs in veins along with pyrite, galena, cinnabar, and realgar, with quartz, calcite or barite as gangue minerals.

Stibnite has been found in Arkansas, California, Nevada, and Utah.

The Nickel Group

Nickel as a metal is silvery-white in color, rather hard, and does not tarnish when exposed to the air. When pure it is malleable and fairly ductile. It is highly useful for plating other metals to protect their surfaces. Alloyed with steel, it makes a product of extreme hardness. Copper, zinc, and nickel make the well known German silver.

Nickel has a fairly large range of minerals, but they do not occur with any abundance in the United States, so that we have to import most all of our nickel. In the earlier days New Caledonia produced most of the world’s supply, but recently since the finding of large nickel deposits near Sudbury, Canada, this locality has 83 not only outstripped New Caledonia, but now produces four-fifths of the world’s supply. In this country but two nickel minerals will be found at all common.

Niccolite NiAs Pl. 25 copper nickel

Occurs in masses; hardness 5.5; specific gravity 7.4; color pale coppery-yellow; streak pale brownish-black; luster metallic; opaque on thin edges.

Niccolite is very seldom in crystals, but if they do occur they are hexagonal. The mineral looks a little like smaltite, but in case there is any question of the determination, dissolve a piece in nitric acid, and if niccolite, it will color the solution green.

Niccolite is usually associated with copper and silver ores, and in this country has been found at Chatham, Conn., and Silver Cliff, Colo. It may be associated with pentlandite, a sulphide of iron and nickel, which is similar in appearance, but not so hard, and occurs in small grains throughout dark lavas. The particles of pentlandite are however so small, that they are seldom noticeable, but at Sudbury, Canada, this is the chief ore of nickel.

Millerite NiS capillary pyrites

Occurs in needle-like or fibrous crystals; hardness 3.5; specific gravity 5.5; color brass-yellow; streak greenish black; luster metallic; opaque on thin edges.

The fibrous crystals of millerite belong to the orthorhombic system. The color and streak suggest pyrite, but the crystals are long and 84 slender, while pyrite is in cubes, octahedrons, etc. If there is any doubt of the identity of this form, place a piece in nitric acid, and if it is millerite, it will color the acid green.

It may occur in veins associated with cobalt and silver minerals, or as a secondary mineral as at Gap Mine, Penn., or in cavities in sedimentary rocks. In the last case it usually is in needle-like crystals growing through calcite crystals, as at St. Louis, Mo., Keokuk, Iowa, and Antwerp, N. Y.

The Cobalt Group

As a metal, cobalt is hard, brittle, and of a grayish color, tinged with red. It was not recognized as a separate element until 1735, and even today is one of the minor metals. Cobalt, chromium and a little tungsten make the alloy stellite, which has come into large use in making high-speed tools. The oxide of cobalt (CoO) is “smalt,” used to give the blue color to porcelain, pottery, glass, tiles, etc. Invisible ink is made by diluting cobalt chloride in a large quantity of water. This solution is a faint pink color and practically invisible on paper, but if heated it loses water and turns blue in color, and is perfectly visible.

Cobalt is another of the metals, of which the United States does not have an adequate supply. Sweden, Norway and India were the chief sources of supply until cobalt was found near the town of Cobalt in Ontario, Canada, and now this district furnishes 90% of the world’s supply.

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Cobaltite CoAsS Pl. 26 cobalt glance

Usually crystalline in cubes, pyritohedrons or octahedrons; hardness 5.5; specific gravity 6.1; color reddish silver-white; streak grayish-black; luster metallic; opaque on thin edges.

In color cobaltite may appear very like arsenopyrite, especially if the reddish tinge is not strong, in which case the mineral can be definitely determined by putting a piece in nitric acid. If it is cobaltite the solution will be colored rose-red, if arsenopyrite there will be no change of color. The forms of the crystals are the same as those of pyrite, but the color will easily distinguish cobaltite from pyrite. This pink color is characteristically present either in or about cobalt minerals, being sometimes called “cobalt bloom.” It is a cobalt-arsenic-oxide with water of crystallization (Co₃As₂O₈·8H₂O), which results from the exposure of cobalt and arsenic minerals to air and moisture. It is the pink color on the figures of both cobaltite and smaltite. In Sweden, Norway and India, this is the chief ore for cobalt, but in the United States it is rather rare, but is found in Oregon, and at Cobalt, Canada.

Smaltite (CoNi)As₂ Pl. 26 gray cobalt ore

Usually occurs in masses; hardness 5.5; specific gravity 6.2; color tin-white to steel-gray; streak grayish-black; luster metallic; opaque on thin edges.

While very like cobaltite, smaltite is almost never found in crystals, but when crystals are found, they are cubes. The color is tin-white 86 but there is usually a pink tinge visible due to the presence of small amounts of “cobalt bloom.” If in any doubt about the determination of this mineral, put a piece in nitric acid. If it colors the acid rose-pink, and is non-crystalline it is pretty surely smaltite; if the acid is not affected it is arsenopyrite.

Smaltite is found in Kentucky, Missouri, Colorado, Idaho, California, and at Cobalt in Canada.

Chromium

This metal gets its name in recognition of the many colors (chroma “color”), in which its compounds appear. Chromic oxide is a vivid green, used to color porcelains, pottery, tiles, etc., and also as a substitute for the arsenical greens formerly used in wall-paper. The chromate of lead is the pigment, well known to artists as “chrome yellow,” and the bichromate of potassium is bright red. The metal is obtained in at least two different forms; one hard, brittle and so resistant to heat as to be infusible at temperatures which would volatilize platinum; the other as a powder which burns brightly if heated in air. While used in paints, dyes, etc., its greatest importance is for the making of ferro-chrome steel, which is used where resistance to sudden shock is required, as in armor plate, automobile springs, ball bearings, etc. With tungsten and cobalt it makes the alloy, stellite, as noted above.

Chromium was used in relatively small quantities 87 before the first world war, and we imported our supplies from Turkey, India, New Caledonia, and Rhodesia. During the last war we started a large-scale development of low-grade ores in Montana, and can now supply all of our needs from this source.

Chromite FeCr₂O₄ chromic iron

Occurs in grains, masses, or isometric octahedrons; hardness 5.5; specific gravity 4.4; color black; streak dark-brown; luster submetallic; opaque on thin edges.

In form, color and streak chromite resembles magnetite and franklinite. From the magnetite it is distinguished by being non-magnetic; from the franklinite, by being insoluble in hydrochloric acid, while the franklinite is soluble. Chromite furnishes practically all the chromium used in the arts and manufactures. It is a mineral associated with high temperatures, and therefore found in dark lavas, serpentine, and olivine. It occurs in Pennsylvania, Maryland, New Jersey, Montana, Oregon, Wyoming, and California.

Tungsten

This element is obtained either as a heavy dark-gray metal, which is very hard and difficult 88 to fuse, or as a dark-gray powder. It is used as an alloy with iron, one part of tungsten to nine of steel, to make the ferrotungsten, which has extraordinary hardness, and is used mostly for high-speed tools. Tungsten is also one of the three metals (cobalt, chromium and tungsten) which are alloyed together to make stellite. Some of the tungsten supply is also used to make the films in incandescent lamps, and in some of the chemical industries. It has but one important ore, wolframite, and this is found in the United States in but small quantities; so that we ordinarily have to import the greater part of what we use. During the last war, under the stimulus of high prices and the urge of necessity, we did find and produce substantial quantities of tungsten. China is the world’s largest producer of tungsten ore with Burma second, and the United States a poor third.

Wolframite (FeMn)WO₄

Occurs in monoclinic crystals or in crystalline masses; hardness 5.5; specific gravity 7.4; color dark-brown to black; streak nearly black; luster submetallic; opaque on thin edges.

If in crystals the form will serve to distinguish this mineral from cassiterite and ilmenite, the two which it most resembles; but if it is massive the only sure way to decide is to put a piece in strong sulphuric acid; if it dissolves and throws down a yellow precipitate (tungstic acid) it is wolframite.

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Like the two other minerals mentioned above it occurs in veins in igneous rocks, being associated with high temperatures. As it is almost insoluble in water, like cassiterite and ilmenite, it is likely to occur with them in the sands which are the result of the disintegration of the rocks which carried the minerals; and so a large part of the supply today comes from placer deposits.

It is found in Connecticut, North Carolina, Missouri, Colorado, and California.

Radium, Uranium and Vanadium

These three metals are all rare and occur together. Radium, discovered in 1898, is a heavy metal which has proved very useful because of its radio-activity, that is, its power of giving off or radiating tiny particles of matter known as X-rays, part of which are charged with positive electricity, and part of them with negative electricity. The ability of these rays to pass through other substances has made possible photographing the denser substances within those less dense, as the bones within the flesh, or metal within leather or wood, etc. The rays have proved of great value medicinally, and are also used to make objects luminous in the dark. These X-rays are also used in the study of the ultimate structure of matter, as it can be thus obtained in such small units.

Uranium is another element which is radio-active and can be used for many of the same purposes as radium.

Vanadium, the third of these associated metals, 90 and the commonest of the group, is not radio-active. It is a silvery-white metal, mostly used as an alloy with steel to give it great hardness.

Carnotite K₂O·2U₂O₃·V₂O₅·3H₂O Pl. 27

Occurs in earthy masses; color yellow.