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The discovery of copper dates back to prehistoric times, and is said to have been mined for more than 5000 years. It is found native and in the minerals cuprite, malachite, azurite, chalcopyrite and bornite and is often a by-product of silver. Of the ores the sulphides, oxides and carbonates are the most of importance.
Copper has a face centred cubic crystal structure. It is yellowish red in physical appearance and takes on a bright metallic luster when polished. It is tough, ductile and malleable. Copper has a disagreeable taste and a peculiar smell.
Copper is the best conductor of electricity next to silver, having a conductivity 97% that of silver.
Copper is generally corrosion-resistant to rural, marine and industrial atmospheres, it is resistant to various waters, saline solutions, soils, non-oxidising mineral and organic acids and caustic solutions. However, copper is attacked by oxidising acids (e.g. nitric), moist ammonia, and halogens, sulphides and solutions containing ammonia ions.
Copper belongs to many series such as, standard wrought grades represented by the designations C10XXX to C15XXX, standard cast coppers represented by the designations C80XXX to C81100 and the highest-purity grade is oxygen-free-electronic copper which is at least 99.99% pure copper.
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