Covellite (also known as covelline) is a rare copper sulfide mineral with the formula CuS. This indigo blue mineral is commonly a secondary mineral in limited abundance and although it is not an important ore of copper itself, it is well known to mineral collectors.
The mineral is generally found in zones of secondary enrichment (supergene) of copper sulfide deposits. Commonly found as coatings on chalcocite, chalcopyrite, bornite, enargite, pyrite, and other sulfides, it often occurs as pseudomorphic replacements of other minerals. The first records are from Mount Vesuvius, formally named in 1832 after N. Covelli.
Covellite belongs to the binary copper sulfides group, which has the formula CuxSy and can have a wide-ranging copper/sulfur ratio, from 1:2 to 2:1 (Cu/S). However, this series is by no means continuous and the homogeneity range of covellite CuS is narrow. Materials rich in sulfur CuSx where x~ 1.1- 1.2 do exist, but they exhibit "superstructures", a modulation of the hexagonal ground plane of the structure spanning a number of adjacent unit cells. This indicates that several of covellite's special properties are the result of molecular structure at this level.
As described for copper monosulfide, the assignment of formal oxidation states to the atoms that constitute covellite is deceptive. The formula might seem to suggest the description Cu2+, S2−. In fact the atomic structure shows that copper and sulfur each adopt two different geometries. However photoelectron spectroscopy, magnetic, and electrical properties all indicate the absence of Cu2+ (d9) ions. In contrast to the oxide CuO, the material is not a magnetic semiconductor but a metallic conductor with weak Pauli-paramagnetism. Thus, the mineral is better described as consisting of Cu+ and S− rather than Cu2+ and S2−. Compared to pyrite with a non-closed shell of S− pairing to form S22−, there are only 2/3 of the sulfur atoms held. The other 1/3 remains unpaired and together with Cu atoms forms hexagonal layers reminiscent of the boron nitride (graphite structure).
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Copper sulfides describe a family of chemical compounds and minerals with the formula CuxSy. Both minerals and synthetic materials comprise these compounds. Some copper sulfides are economically important ores. Prominent copper sulfide minerals include Cu2S (chalcocite) and CuS (covellite). In the mining industry, the minerals bornite or chalcopyrite, which consist of mixed copper-iron sulfides, are often referred to as "copper sulfides". In chemistry, a "binary copper sulfide" is any binary chemical compound of the elements copper and sulfur.
The sulfide minerals are a class of minerals containing sulfide (S2−) or disulfide (S22−) as the major anion. Some sulfide minerals are economically important as metal ores. The sulfide class also includes the selenides, the tellurides, the arsenides, the antimonides, the bismuthinides, the sulfarsenides and the sulfosalts. Sulfide minerals are inorganic compounds.
Bornite, also known as peacock ore, is a sulfide mineral with chemical composition that crystallizes in the orthorhombic system (pseudo-cubic). Bornite has a brown to copper-red color on fresh surfaces that tarnishes to various iridescent shades of blue to purple in places. Its striking iridescence gives it the nickname peacock copper or peacock ore. Bornite is an important copper ore mineral and occurs widely in porphyry copper deposits along with the more common chalcopyrite.
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