Covellite
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2008-06-22T12:03:55Z
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{{Infobox mineral
| name = Covellite
| category = [[Sulfide mineral]]
| boxwidth =
| boxbgcolor =
| image =CovelliteByu00432.jpg
| caption =
| formula = [[copper]] [[sulfide]]:[[copper sulfide|CuS]]
| molweight =
| color = Indigo blue (tarnished to purple or black)
| habit = thin platy hexagonal crystals also massive to granular.
| system = [[Hexagonal]] 6/m2/m2/m
| twinning =
| cleavage = Perfect in one direction
| fracture = flakey
| mohs = 1.5 - 2
| luster = metallic
| refractive = opaque
| opticalprop =
| birefringence =
| pleochroism =
| streak = lead gray to black
| gravity = 4.6 - 4.8
| melt =
| fusibility = 2.5
| diagnostic =
| solubility =
| diaphaneity =
| other = micaceous cleavage
}}
[[Image:Cp--Covellite.jpg|thumb|right|Covellite (gray) replacing and embaying chalcopyrite (light), polished section from Horn Silver Mine, [[San Francisco Mining District]], [[Utah]]. Enlarged 210 diameters]]
'''Covellite''' (also known as covelline) is a rare [[copper sulfide]] mineral with the [[chemical formula|formula]] CuS. This indigo blue mineral was the first discovered natural [[superconductor]]<ref name=Ben2006>{{cite journal
| title = First evidence of natural superconductivity
| author = Benedetto, F.D., Borgheresi, M., Caneschi, A., Chastanet, G., Cipriani, C., Gatteschi, D., Pratesi, G., Romanelli, M., Sessoli, R.
| journal = [[European Journal of Mineralogy]]
| volume = 18
| issue = 3
| pages = 283–287
| year = 2006
| url =
| doi = 10.1127/0935-1221/2006/0018-0283 }}</ref>. Because of it limited abundance, it is not an important copper ore, although it is well known to mineral collectors.
As described for the mineral [[pyrite]], the assignment of formal oxidation states (or charges) to the atoms that constitute covellite is deceptive. The formula might seem to suggest the description Cu<sup>2+</sup>, S<sup>2-</sup>. In fact the atomic structure shows that copper and sulfur each adopt two different geometries. Thus, the mineral is probably best described as consisting of both Cu<sup>2+</sup>, S<sup>2-</sup> and 2Cu<sup>+</sup>, S<sub>2</sub><sup>2-</sup>.
The mineral is associated with chalcosite in zones of secondary enrichment ([[Supergene (geology)|supergene]]) of copper sulfide deposits. Commonly found with and as coatings on [[chalcocite]], [[chalcopyrite]], [[bornite]], [[enargite]], [[pyrite]], and other sulfides. It often occurs as pseudomorphic replacements after other minerals. Very rare occurrence as a volcanic sublimate at Mount Vesuvius the site of its discovery or first description by [[Nicola Covelli]] (1790 - 1829).
===Composition===
Covellite (CuS) belongs to the binary copper sulfides group, which has the formula Cu<sub>x</sub>S<sub>y</sub> and can have a wide-ranging copper/sulfur ratio from 1:2 to 2:1 (Cu/S) <ref name=Sie2006>{{cite journal
| title = Copper(II) sulfide?
| author = Siew Wei Goh, Alan N. Buckley, Robert N. Lamb
| journal = [[Minerals Engineering]]
| volume = 19
| issue = 2
| pages = 204–208
| year = 2006
| url =
| doi = 10.1016/j.mineng.2005.09.003 }}</ref>. Although the fundamental structure of covellite is CuS, research into its "superstructure" (large numbers of adjoined of CuS molecules) indicates that several of covellite's special properties are the result of molecular structure at this level<ref>{{cite journal
| title = Blaubleibender covellite and its relationship to normal covellite
| author = Putnis, A., Grace, J. and Cameron, W.E.
| journal = [[Contributions to Mineralogy and Petrology]]
| volume = 60
| issue = 2
| pages = 209–217
| year = 1977
| url =
| doi = 10.1007/BF00372282 }}
</ref>. Both Cu<sup>+</sup> and Cu<sup>2+</sup> cations are included as part of the minerals "superstructure", resulting in an elemental composition of 2Cu<sup>+</sup>, Cu<sup>+2</sup> and S<sup>-2</sup> <ref name=Sie2006/>
===Formation===
Covelite is commonly found as secondary copper mineral in deposits, more rarely as a primary mineral in copper deposits, and very rare as [[volcanic]] [[sublimate]]. Covellite is known to form in [[weathering]] environments near the surface in deposits where copper is the primary sulfide. As a primary mineral, the formation of covellite is restricted to [[hydrothermal]] conditions.
Covellite's unique crystal structure are related to the conditions of its formation. The covellite (Cu<sub>x</sub>S<sub>y</sub>) framework of CuS<sub>3</sub> planes which are isolated by electronegatively charged CuS<sub>2</sub> planes. This distinct framework is produced during oxidative formation conditions. Attempts to synthesize covellite <ref name=Sim2007>{{cite journal
| title = Thermal behaviour of CuS (covellite) obtained from copper–thiosulfate system
| author = Simonescu, C.M., Teodorescu, V.S., Carp, O., Patron, L. and Capatina, C.
| journal = [[Journal of Thermal Analysis and Calorimetry]]
| volume = 88
| issue = 1
| pages = 71–76
| year = 2007
| url =
| doi = 10.1007/s10973-006-8079-z }}</ref><ref>{{cite journal
| title = Nickel sulfide and copper sulfide nanocrystal synthesis and polymorphism
| author = Ghezelbash A, Korgel BA.
| journal = Langmuir
| volume = 21
| issue = 21
| pages = 9451–9456
| year = 2005
| url =
| doi = 10.1021/la051196p S0743-7463(05)01196-0 }}</ref> indicate it undergoes a complex [[oxidation]] process, and that its formation depends on the state and history of the associated sulfides it was derived from. Experimental evidence <ref name=Sim2007/> shows ammonium metavanadate (NH<sub>4</sub>VO<sub>3</sub>) to be a potentially important [[catalyst]] for covellite's solid state transformation from other copper sulfides.
===Geologic occurrence===
Covellite's occurrence is widespread and some of the highest quality specimens have been found in the United States. In [[Silver Bow County, Montana]], covellite has been found in veins at depths of 1,150 meters, as the primary mineral. Covellite formed as clusters in these [[Vein (geology)|veins]] reaching one meter across in [[Leonard mines, Montana]].<ref>Cook, R.B., Covellite: Summitville, Rio Grande County, Colorado. Rocks & Minerals. 296-300. 2006.</ref> As a secondary mineral, covellite also forms as descending surface water in the [[Supergene (geology)|supergene]] enrichment zone oxidizes and redeposits covellite on [[hypogene]] sulfides (pyrite and chalcopyrite). Locally, findings of covellite have been discovered in [[salt domes]] and at the [[McCellan copper mine]] in [[Foard County, Texas]]. The finest mineral specimens of covellite come from [[Rio Grande County, Colorado]]. Beautiful colors of deep blue covellite and bright metallic pyrite forms hexagonal plates 2cm across. An unusual occurrence of covellite was found replacing organic debris in the [[red bed]]s of [[New Mexico]]. Another interesting occurrence of covellite is in [[Maska, Lebanon]]. Covellite is one of two major [[ore]] minerals that have been mined where the major component is mineral ice. A high-grade ore [[outcrop]] weathered and debris settle into adjacent [[glaciers]] producing 200,000 tons of ore.{{Fact|date=December 2007}}
===Applications===
Covellite was the first discovered natural [[superconductor]]<ref name=Ben2006/> The framework of CuS<sub>3</sub> /CuS<sub>2</sub> allow for an electron excess that facilitate superconduction during particular states, with exceptionally low thermal loss. Material science is now aware of several of covellites favorable properties and several researchers are intent on sythesizing covellite <ref>{{cite journal
| title = Complex Concaved Cuboctahedrons of Copper Sulfide Crystals with Highly Geometrical Symmetry Created by a Solution Process
| author = Chunyan Wu, Shu-Hong Yu, and Markus Antoniette
| journal = [[Chemistry Of Materials]]
| volume = 18
| issue = 16
| pages = 3599–3601
| year = 2006
| url =
| doi = 10.1021/cm060956u S0897-4756(06)00956-2}}</ref><ref>{{cite journal
| title = Electrochemical characterization of chemical species formed during the electrochemical treatment of chalcopyrite in sulfuric acid
| author = Nava, Dora , Gonzalez, I, et al.
| journal = [[Electrochimica Acta]]
| volume = 51
| issue = 25
| pages = 5295–5303
| year = 2006
| url =
| doi = 10.1016/j.electacta.2006.02.005}}</ref>. Gramp et al. (2006) discovered that covellite can also be produced in the lab under [[anaerobic]] conditions by sulfate reducing bacteria at a variety of temperatures. However, further research remains, because although the abundance of covellite may be high, the growth of its crystal size is actually inhibited by physical constraints of the bacteria <ref>{{cite journal
| title = Formation of Covellite (CuS) Under Biological Sulfate-Reducing Conditions
| author = Gramp, J.P., Sasaki, K., Bigham, J.M., Karnachuck, O.V., Tuovinen, O.H.
| journal = [[Geomicrobiology Journal]]
| volume = 23
| issue = 8
| pages = 613 – 619
| year = 2006
| url =
| doi = 10.1080/01490450600964383 }}</ref>. It has been experimentally demonstrated that the presence of ammonium vanadates is important in the solid state transformation of other copper sulfides to covellite crystals <ref name=Sim2007/>
==See also==
*[[List of minerals]]
*[[List of minerals named after people]]
== References ==
{{Reflist}}*Dana's Manual of Mineralogy ISBN 0-471-03288-3
*[http://mineral.galleries.com/minerals/sulfides/covellit/covellit.htm Mineralgalleries.com]
*[http://webmineral.com/data/Covellite.shtml Webmineral]
*[http://www.mindat.org/min-1144.html Mindat.org]
[[Category:Copper minerals]]
[[Category:Sulfide minerals]]
[[ca:Covel·lita]]
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[[nl:Covellien]]
[[ja:銅藍]]
[[sk:Covellit]]
[[uk:Ковелін]]
[[zh:銅藍]]