Bornite

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bornite

[′bȯr‚nīt]
(mineralogy)
Cu5FeS4 A primary mineral in many copper ore deposits; specific gravity 5.07; the metallic and brassy color of a fresh surface rapidly tarnishes upon exposure to air to an iridescent purple.

Bornite

 

(named after the Austrian metallurgist and mineralogist I. Born, 1742–91), a mottled copper ore, a mineral and a sulfide of copper and iron corresponding to the formula CusFeS4. It contains 52–65 percent copper and 8–12 percent iron. It crystallizes into a cubic system; a modification of a rhombic system is known. Its crystalline structure is of the spinel type. Crystals (cubic or dodecahedral habits) are rare; dense grainy masses are common. They are dark colored, copper red, usually with bright mottled oxide tint in old fractures. Its hardness on the mineralogical scale is 3, and its density is 4,900–5,300 kg/m3.

Bornite is of varying origin. As a hypogene mineral, it is formed in various types of hypothermal deposits. During supergene processes, it is formed in the zone of secondary sulfide concentration. Evolutions of supergene bornite are found in sedimentary rocks, sometimes in the form of pseudomorphoses by organic residues. In hydrothermal deposits, bornite usually is found in association with chalcopy-rite, pyrite, sphalerite, and fahlerz (gray copper ore). It is observed rather frequently in deposits of the type of pyrite seams. Malachite, azurite, cuprite, and other minerals are formed from bornite in oxidation zones. Bornite is an important mineral of copper ores. Deposits of bornite in the USSR are found in the Urals, in the Caucasus, and in Kazakhstan; they are found abroad in the USA, Yugoslavia, South West Africa, and the German Democratic Republic.