.

Copper Mineral Facts:

Chemical Formula: Cu

Colors: Copper Red
Often dark and with a dull luster on account of tarnish.

Hardness: 2.5 to 3
Hardness varies somewhat depending on formation and impurities.

Density: 8.8 to 8.9

Cleavage: None

 Crystallography: Isometric
Usually in irregular masses, plates, scales, etc., in twisted and wire like forms. Tetrahexahedron faces common on crystals. Also cube and dodecahedron. Groups of crystals are very common. Crystals usually distorted and in branching and arborescent groups, often they are skeleton crystals. In spite of its softness copper is better crystallized than either gold or silver.

Luster:. Metallic luster.

Optics: (Refractive Index):  Opaque

Above: Native Copper, Nevada

Composition, Structure and Associated Minerals:
Metallic copper is 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. Most of the copper of commerce is obtained from one or the other of its sulfides. Some, however, is found as the native metal. Copper, often contains small amounts of silver, bismuth, mercury, etc. It is highly ductile and malleable.

Identification and Diagnostics
Copper may easily be distinguished from all other substances except gold and a few alloys by its malleability and color. Fuses at 3 to a globule, which becomes covered with an oxide coating on cooling. Dissolves readily in nitric acid, with the evolution of brownish red fumes of nitrous oxide gas. The solution is colored a deep blue on addition of ammonium hydroxide in excess. It is an excellent conductor of electricity.

Occurrence, Localities and Origins:
Occurrence. The principal modes of occurrence of the metal are, (i) as fine particles disseminated through sandstones and slates, (2) as solid masses filling the spaces between the pebbles and boulders making up the rock known as conglomerate, (3) in the cavities in old volcanic lavas, known as amygdaloid, (4) as crystals or groups of crystals imbedded in the calcite of veins, (5) in quartz veins cutting old igneous rocks or schists, and (6) associated with the carbonates, malachite and azurite, and with its different sulfur compounds, in the weathered zone of many veins of copper ores.

The copper that occurs in the upper portions of veins of copper sulfides is plainly of secondary origin. That which occurs in conglomerates and other fragmental rocks and in amygdaloids was evidently deposited by water, but whether by ascending magmatic water or by descending meteoric water is a matter of doubt.

Localities. Native copper is found in Cornwall, England, in Nassau, Germany, in Bolivia, Peru, Chile and other South American countries, in the Appalachian region of the United States and in the Lake Superior region, both on the Canadian and the American sides. The most important district in the world producing native copper is on Keweenaw Point, in Michigan. The mineral occurs mainly in a bed of conglomerate of which it constitutes from 1 to 3 per cent, though it is found abundantly also in sandstone and in the amygdaloidal cavities of lavas associated with the conglomerates. Veins of calcite, through which groups of bright copper crystals are scattered are also very plentiful in many parts of the district. The copper is often mixed with silver in visible grains and patches. 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.

Return to the Mineral Collectors Information Page

Above: Copper Specimen, Michigan

Nevada Outback Gems