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, 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 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 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.
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 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.