Copper Composition, Crystallization, Structure and Occurrence
Composition. Copper, often containing small amounts of silver, bismuth, mercury, etc.
Crystallization. Isometric. Tetrahexahedron faces common on crystals. Also cube and dodecahedron. Crystals usually distorted and in branching and arborescent groups.
Structure. Usually in irregular masses, plates, scales, etc. in twisted and wirelike forms.
Physical Properties. H. = 2.5-3. G. = 8.8 – 8.9. Highly ductile and malleable. Color copper-red, usually dark and with a dull luster on account of tarnish.
Test. Fuses at 3 to a globule, which becomes covered with an oxide coating on cooling. Dissolves readily in nitric acid, and the solution is colored a deep blue on addition of ammonium hydroxide in excess.
Occurrence. A mineral found widely distributed in copper veins, but usually in small amount. Associated with various copper minerals, most commonly with the oxidized ores, cuprite, malachite and azurite. Ordinarily is strictly a secondary mineral and is to be found only in the upper parts of cooper veins.
The most notable deposited of native copper known in the world is on Keweenaw Peninsula in northern Michigan, on the southern shore of Lake Superior. The regions is occupied by a series of igneous flows of traps rock interbedded with sandstone conglomerates. The whole series dips toward the north. The copper is found in veins intersecting this rock series; in the amygdaloidal belts at the top of the various trap flows; and as a cementing material in the sand stone conglomerate. This last type has furnished the most important ore deposits, some of which have been worked for considerably over a mile in vertical depth. Not only does the copper act as a cement to bind the conglomerate together, but it has often penetrated the quartz boulders of the rock to a depth of a foot or more. It is associated with such minerals as epidote, datolite, calcite and various zeolites. The mines were worked superficially by the Indians, and have been actively developed since the middle of the eighteenth century. Most of the copper of the district occurs in very small irregular specks, but notable large, masses have been found, one weighing 420 tons being discovered in 1857.
Sporadic occurrences of copper similar to that of the Lake Superior District have been found in the sandstone areas of the eastern United States, notably in New Jersey, and in the glacial drift overlying a similar area in Connecticut. Native copper occurs in small amounts, associated with the oxidized ores of Arizona, New Mexico and northen Mexico.
Use. The most important uses to which the metal is put are as an electrical conductor; in the manufacture of brass (an alloy of copper and zinc); of bronze (an alloy of copper and tin with frequently zinc); for sheet copper; and as copper sulphate, which is used in calico printing, in galvanic cells, etc.
Mercury, Ampalgam (Ag, Hg) and Lead are rare metals.
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