COMMON MINERALS AND VALUABLE ORES.
IV.—COPPER AND LEAD ORES.
THEO. F. BROOKINS, B. S.
THE first metal that was employed by man is copper. It is probable that prehistoric man made use of the metal in its native condition only, as no knowledge of metallurgy would be essential in preparing it for use from that condition. Copper implements have been found in the lake dwellings of Switzerland, and bronze, an alloy of copper and tin, is mentioned in the writings of Homeric times.
Cuprum, the origin of our English word copper, is derived from cyprium, which refers to the occurrence of the metal in especial abundance on the island of Cyprus, the main source of the metal during the epochs of early alchemy. In the Hebrew scriptures copper is termed Nehósheth (from nahásh, meaning to glisten) which is translated by Χαλκος and by Aes in the Vulgate. Later Aes cyprium was the special designation, which was finally shortened to cyprium, as indicated above. Thus we see that our present term represents in no sense the characteristic of the metal at first so noticeable.
Native copper scarcely needs a description. Its occurrence in the free state provides an interesting subject of conjecture. Briefly stated, the question of origin is whether the copper was set free by the decomposition of silicates or was in the form of a sulphide in the rock. The chief region of occurrence of native copper is the Lake Superior district. Here are found occasionally large masses of copper, which, strange as it seems, are practically valueless if too heavy to transport, since they cannot be divided without great difficulty. Of the world's total output of copper in 1897, 399,250 long tons [2], a single mine of the Lake Superior region, the famous Calumet and Hecla, produced 40,350 long tons.
Montana is now the first copper producing state in the United States. The state contains the largest mining camp in the world, located in the town of Butte. In 1897 the mines of Montana produced 102,800 long tons of copper. The ore chalcocite, sometimes called copper glance, has a metallic luster, often tarnished green or blue. It is commonly lead-gray and rather soft. Its streak is a blackish lead-gray, Chalcopyrite, a sulphide of copper and iron combined, has already been mentioned under "Iron Minerals" ([November issue of Birds and All Nature].) When copper is much in predominance the color of the ore is golden yellow. The streak is dark green. The mineral is harder than chalcocite, but less hard than pyrite, being easily scratched with a knife. Both chalcocite and chalcopyrite frequently occur in silver-bearing rocks.
A method of extracting copper from its ores, equally useful with regard to any of the ores, is known as the English process. The details of this are too elaborate and technical for consideration here. In brief, the process consists of six distinct parts—roasting the mixed ores, fusion of the roasted ores to produce coarse metal, roasting the coarse metal, fusion of the wasted coarse metal to produce what is known as white metal, roasting of the white metal to produce blister copper, i. e., copper filled with cavities, and finally the refining and toughening of the blister copper until marketable copper is yielded. The English method of copper smelting is classed among the so-called "dry" processes, in contradistinction from "wet" processes, or methods involving the use of solutions.
It may be of interest to know the importance of copper in that curious problem of ancient alchemy, the transmutation of metals. Metallic iron placed in certain solutions of unknown composition possessed the power to precipitate metallic copper. With all the wondrous faith in the problems of alchemy the phenomenon was interpreted as one of transmutation and the statement made that iron had been transformed into copper.