Editing Covellite

{{Short description|Sulfide mineral}}
{{Infobox mineral
| name        = Covellite
| category    = [[Sulfide mineral]]
| boxwidth    = 
| boxbgcolor  = 
| image       = Covellite-252597.jpg
| imagesize   = 260px
| caption     = 
| formula     = CuS ([[copper monosulfide]])
| IMAsymbol   = Cv<ref>{{Cite journal|last=Warr|first=L.N.|date=2021|title=IMA–CNMNC approved mineral symbols|journal=Mineralogical Magazine|volume=85|issue=3|pages=291–320|doi=10.1180/mgm.2021.43|bibcode=2021MinM...85..291W|s2cid=235729616|doi-access=free}}</ref>  
| molweight   = 
| strunz      = 2.CA.05a
| dana        = 02.08.12.01
| system      = [[Hexagonal crystal system|Hexagonal]] 
| class       = Dihexagonal dipyramidal (6/mmm) <br/>[[H–M Symbol]] (6/m 2/m 2/m)
| symmetry    = ''P''6<sub>3</sub>/mmc
| unit cell   = a = 3.7938&nbsp;Å, c = 16.341&nbsp;Å; Z&nbsp;=&nbsp;6
| color       = Indigo-blue or darker, commonly highly iridescent, brass-yellow to deep red
| habit       = Thin platy hexagonal crystals and rosettes also massive to granular.
| twinning    = 
| cleavage    = Perfect on {0001}
| fracture    = 
| tenacity    = Flexible 
| mohs        = 1.5–2
| luster      = Submetallic, inclining to resinous to dull
| refractive  = n<sub>ω</sub> = 1.450 n<sub>ε</sub> = 2.620
| opticalprop = Uniaxial (+)
| birefringence = 
| pleochroism = Marked, deep blue to pale blue
| streak      = Lead gray
| gravity     = 4.6–4.8
| melt        = 
| fusibility  = 2.5
| diagnostic  = 
| solubility  = 
| diaphaneity = Opaque
| other       = Micaceous cleavage
| references  = <ref name=Handbook>[http://rruff.geo.arizona.edu/doclib/hom/covellite.pdf Handbook of Mineralogy]</ref><ref name=Webmin>[http://webmineral.com/data/Covellite.shtml Webmineral data]</ref><ref name=Mindat>[http://www.mindat.org/min-1144.html Mindat.org]</ref>
}}

[[Image:Cp--Covellite.jpg|thumb|Covellite (gray) replacing and embaying chalcopyrite (light), polished section from Horn Silver Mine, San Francisco Mining District, [[Utah]]. Enlarged to 210 diameters. |alt=]]
'''Covellite''' (also known as '''covelline''') is a rare [[copper sulfide]] mineral with the [[chemical formula|formula]] CuS.<ref name="Mindat" /> 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.<ref name="Mindat" />

The mineral is generally found in zones of secondary enrichment ([[Supergene (geology)|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.<ref>{{Cite book|title=Chlorine Compounds-Advances in Research and Application|last=Q. Ashton Acton|date=2012|publisher=ScholarlyMedia LLC|isbn=9781481600040|oclc=1024280169}}</ref> The first records are from [[Mount Vesuvius]], formally named in 1832 after N. Covelli.<ref name=Mindat/>

==Composition==
Covellite 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). However, this series is by no means continuous and the homogeneity range of covellite CuS is narrow. Materials rich in sulfur CuS<sub>x</sub> where x~ 1.1- 1.2 do exist, but they exhibit "[[Superstructure (condensed matter)|superstructures]]", a modulation of the hexagonal ground plane of the structure spanning a number of adjacent unit cells.<ref>{{Cite journal|last1=Putnis|first1=A.|last2=Grace|first2=J.|last3=Cameron|first3=W. E.|date=1977|title=Blaubleibender covellite and its relationship to normal covellite|journal=Contributions to Mineralogy and Petrology|volume=60|issue=2|pages=209–217|doi=10.1007/bf00372282|bibcode=1977CoMP...60..209P|s2cid=95661500|issn=0010-7999}}</ref> 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 state|oxidation states]] to the atoms that constitute covellite is deceptive.<ref name=":8">{{Cite journal|last1=Evans|first1=Howard T.|last2=Konnert|first2=Judith A.|date=1976|title=Crystal structure refinement of covellite|journal=American Mineralogist|volume=61|pages=996–1000}}</ref> 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. However [[photoelectron spectroscopy]], [[Magnetism|magnetic]], and [[electrical]] properties all indicate the ''absence'' of Cu<sup>2+</sup> (d<sup>9</sup>) ions.<ref name=":8" /> In contrast to the oxide CuO, the material is not a magnetic [[semiconductor]] but a metallic conductor with weak [[Pauli paramagnetism|Pauli-paramagnetism]].<ref name=":9">{{Cite book|title=Synthesis, properties and mineralogy of important inorganic materials|last=Warner, Terence E.|date=2013|publisher=Wiley|isbn=9780470976234|oclc=865009780}}</ref> Thus, the mineral is better described as consisting of Cu<sup>+</sup> and S<sup>−</sup> rather than Cu<sup>2+</sup> and S<sup>2−</sup>. Compared to pyrite with a non-closed shell of S<sup>−</sup> pairing to form S<sub>2</sub><sup>2−</sup>, there are only 2/3 of the sulfur atoms held.<ref name=":8" /> The other 1/3 remains unpaired and together with Cu atoms forms hexagonal layers reminiscent of the boron nitride (graphite structure).<ref name=":8" /> Thus, a description Cu<sup>+</sup><sub>3</sub>S<sup>−</sup>S<sub>2</sub><sup>2−</sup> would seem appropriate with a delocalized hole in the [[valence band]] leading to metallic conductivity. Subsequent band structure calculations indicate however that the hole is more localized on the sulfur pairs than on the unpaired sulfur. This means that Cu<sup>+</sup><sub>3</sub>S<sup>2−</sup>S<sub>2</sub><sup>−</sup> with a mixed sulfur oxidation state −2 and −1/2 is more appropriate. Despite the extended formula of Cu<sup>+</sup><sub>3</sub>S<sup>2−</sup>S<sub>2</sub><sup>−</sup> from researchers in 1976 and 1993, others have come up with variations, such as Cu<sup>+</sup><sub>4</sub>Cu<sup>2+</sup><sub>2</sub>(S<sub>2</sub>)<sub>2</sub>S<sub>2</sub>.<ref>{{Cite book|title=The relationship between crystal structure, bonding and cell dimensions in the copper sulfides : supplementary unpublished material|last=Goble, Ronald J.|date=1985|oclc=45557917}}</ref><ref name=":3">{{Cite journal|last1=Liang|first1=W.|last2=Whangbo|first2=M.-H.|date=February 1993|title=Conductivity anisotropy and structural phase transition in Covellite CuS|journal=Solid State Communications|volume=85|issue=5|pages=405–408|doi=10.1016/0038-1098(93)90689-k|issn=0038-1098|bibcode=1993SSCom..85..405L}}</ref>

== Structure ==
For a copper sulfide, covellite has a complicated lamellar structure, with alternating layers of CuS and Cu<sub>2</sub>S<sub>2</sub> with copper atoms of trigonal planar (uncommon) and tetrahedral coordination respectively.<ref name=":3" /> The layers are connected by S-S bonds (based on Van der Waals forces) known as S<sub>2</sub> dimers.<ref name=":3" /> The Cu<sub>2</sub>S<sub>2</sub> layers only has one l/3 bond along the c-axis (perpendicular to layers), thus only one bond in that direction to create a perfect cleavage {0001}.<ref name=":8" /> The conductivity is greater across layers due to the partially filled 3p orbitals, facilitating electron mobility.<ref name=":3" />

==Formation==
[[File:Covellite and Pyrite (V).jpg|thumb|A microscopic picture of covellite]]

=== Naturally occurring ===
Covellite is commonly found as a secondary copper mineral in deposits. Covellite is known to form in [[weathering]] environments in surficial deposits where copper is the primary sulfide.<ref>{{Cite journal|last1=Majzlan|first1=Juraj|last2=Kiefer|first2=Stefan|last3=Herrmann|first3=Julia|last4=Števko|first4=Martin|last5=Sejkora|first5=Jiří|last6=Chovan|first6=Martin|last7=Lánczos|first7=Tomáš|last8=Lazarov|first8=Marina|last9=Gerdes|first9=Axel|date=June 2018|title=Synergies in elemental mobility during weathering of tetrahedrite [(Cu,Fe,Zn)12(Sb,As)4S13]: Field observations, electron microscopy, isotopes of Cu, C, O, radiometric dating, and water geochemistry|journal=Chemical Geology|volume=488|pages=1–20|doi=10.1016/j.chemgeo.2018.04.021|issn=0009-2541|bibcode=2018ChGeo.488....1M|s2cid=135253715}}</ref> As a primary mineral, the formation of covellite is restricted to [[hydrothermal]] conditions, thus rarely found as such in copper ore deposits or as a volcanic sublimate.<ref name=":9" />

=== Synthetic ===
Covellite's unique crystal structure is related to its complex [[oxidative]] formation conditions, as seen when attempting to synthesize covellite.<ref name="Sim2007">{{cite journal|author=Simonescu, C.M., Teodorescu, V.S., Carp, O., Patron, L. and Capatina, C.|year=2007|title=Thermal behaviour of CuS (covellite) obtained from copper–thiosulfate system|journal=[[Journal of Thermal Analysis and Calorimetry]]|volume=88|issue=1|pages=71–76|doi=10.1007/s10973-006-8079-z|s2cid=94104147}}</ref><ref name=":0">{{Cite journal|last1=Ghezelbash|first1=Ali|last2=Korgel|first2=Brian A.|date=October 2005|title=Nickel Sulfide and Copper Sulfide Nanocrystal Synthesis and Polymorphism|journal=Langmuir|volume=21|issue=21|pages=9451–9456|doi=10.1021/la051196p|pmid=16207021|issn=0743-7463}}</ref> Its formation also depends on the state and history of the associated sulfides it was derived from. Experimental evidence 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.<ref name=":0" /> Researchers discovered that covellite can also be produced in the lab under [[Hypoxia (environmental)|anaerobic]] conditions by sulfate reducing bacteria at a variety of temperatures.<ref name=":1">{{cite journal|author1=Gramp, J.P.|author2=Sasaki, K.|author3=Bigham, J.M.|author4=Karnachuck, O.V.|author5=Tuovinen, O.H.|year=2006|title=Formation of Covellite (CuS) Under Biological Sulfate-Reducing Conditions|journal=[[Geomicrobiology Journal]]|volume=23|issue=8|pages=613–619|doi=10.1080/01490450600964383|s2cid=95152748}}</ref> 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 name=":1" /> 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" />

==Occurrence==
[[File:Covellin - Grube Clara.jpg|thumb|Covellite from the [[Black Forest]], [[Germany]]]]

Covellite's occurrence is widespread around the world, with a significant number of localities in [[Central Europe]], [[China]], [[Australia]], [[Western United States]], and [[Argentina]].<ref name="Mindat" /> Many are found close to [[orogenic belts]], where [[orographic precipitation]] often plays a role in weathering. An example of primary mineral formation is in hydrothermal veins at depths of 1,150 m found in Silver Bow County, Montana.<ref name="Mindat" /> 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) at the same locality.<ref name="Mindat" /> An unusual occurrence of covellite was found replacing [[Organic material|organic debris]] in the [[Red bed|red beds]] of [[New Mexico]].<ref>Emmons, W. H., ''The Enrichment of Ore Deposits,'' Bulletin 625, United States Geological Survey, 1917, p. 193</ref> 

Nicola Covelli (1790-1829), the discoverer of the mineral, was a professor of botany and chemistry though was interested in geology and volcanology, particularly Mount Vesuvius' eruptions.<ref name="Mindat" /> His studies of its lava led to the discovery of several unknown minerals including covellite.<ref name="Mindat" />

==Applications==

=== Superconductors ===
Covellite was the first identified naturally occurring [[superconductor]].<ref name="Ben2006">{{cite journal|author1=Benedetto, F.D.|author2=Borgheresi, M.|author3=Caneschi, A.|author4=Chastanet, G.|author5=Cipriani, C.|author6=Gatteschi, D.|author7=Pratesi, G.|author8=Romanelli, M.|author9=Sessoli, R.|year=2006|title=First evidence of natural superconductivity|journal=[[European Journal of Mineralogy]]|volume=18|issue=3|pages=283–287|bibcode=2006EJMin..18..283D|doi=10.1127/0935-1221/2006/0018-0283}}</ref> 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 covellite's favorable properties and several researchers are intent on synthesizing covellite.<ref>{{cite journal|author1=Chunyan Wu|author2=Shu-Hong Yu|author3=Markus Antoniette|year=2006|title=Complex Concaved Cuboctahedrons of Copper Sulfide Crystals with Highly Geometrical Symmetry Created by a Solution Process|journal=[[Chemistry of Materials]]|volume=18|issue=16|pages=3599–3601|doi=10.1021/cm060956u}}</ref><ref>{{cite journal|last1=Nava|first1=Dora|last2=Gonzalez|first2=I|display-authors=etal|year=2006|title=Electrochemical characterization of chemical species formed during the electrochemical treatment of chalcopyrite in sulfuric acid|journal=[[Electrochimica Acta]]|volume=51|issue=25|pages=5295–5303|doi=10.1016/j.electacta.2006.02.005}}</ref> Uses of covellite CuS superconductivity research can be seen in [[Lithium battery|lithium batteries]]’ [[cathode]]s, [[ammonium]] [[gas sensors]], and [[Solar electric|solar electric devices]] with metal [[chalcogenide]] thin films.<ref>{{Cite journal|last1=Chung|first1=J.-S.|last2=Sohn|first2=H.-J.|date=June 2002|title=Electrochemical behaviors of CuS as a cathode material for lithium secondary batteries|journal=Journal of Power Sources|volume=108|issue=1–2|pages=226–231|doi=10.1016/s0378-7753(02)00024-1|issn=0378-7753|bibcode=2002JPS...108..226C}}</ref><ref>{{Cite journal|last1=Sagade|first1=Abhay A.|last2=Sharma|first2=Ramphal|date=July 2008|title=Copper sulphide (CuxS) as an ammonia gas sensor working at room temperature|journal=Sensors and Actuators B: Chemical|volume=133|issue=1|pages=135–143|doi=10.1016/j.snb.2008.02.015|issn=0925-4005}}</ref><ref>{{Cite journal|last1=Mane|first1=R. S.|last2=Lokhande|first2=C. D.|date=2010-06-03|title=ChemInform Abstract: Chemical Deposition Method for Metal Chalcogenide Thin Films|journal=ChemInform|volume=31|issue=34|pages=no|doi=10.1002/chin.200034236|issn=0931-7597}}</ref>

===Lithium ion batteries===

Research into alternate cathode material for [[lithium batteries]] often examines the complex variations in stoichiometry and [[Tetrahedron packing|tetrahedron]] layered structure of copper sulfides.<ref>{{Cite journal|last1=Foley|first1=Sarah|last2=Geaney|first2=Hugh|last3=Bree|first3=Gerard|last4=Stokes|first4=Killian|last5=Connolly|first5=Sinead|last6=Zaworotko|first6=Michael J.|last7=Ryan|first7=Kevin M.|date=2018-03-24|title=Copper Sulfide (Cu x S) Nanowire‐in‐Carbon Composites Formed from Direct Sulfurization of the Metal‐Organic Framework HKUST‐1 and Their Use as Li‐Ion Battery Cathodes|journal=Advanced Functional Materials|volume=28|issue=19|pages=1800587|doi=10.1002/adfm.201800587|s2cid=104176144 |issn=1616-301X}}</ref> Advantages include limited toxicity and low costs.<ref name=":02">{{Cite journal|last1=Zhou|first1=Mingjiong|last2=Peng|first2=Na|last3=Liu|first3=Zhen|last4=Xi|first4=Yun|last5=He|first5=Huiqiu|last6=Xia|first6=Yonggao|last7=Liu|first7=Zhaoping|last8=Okada|first8=Shigeto|date=February 2016|title=Synthesis of sub-10 nm copper sulphide rods as high-performance anode for long-cycle life Li-ion batteries|journal=Journal of Power Sources|volume=306|pages=408–412|doi=10.1016/j.jpowsour.2015.12.048|bibcode=2016JPS...306..408Z|issn=0378-7753}}</ref> The high [[electrical conductivity]] of covellite (10−3 S cm−1) and a high theoretical [[Capacity factor|capacity]] (560 mAh g−1) with flat discharge curves when cycled versus Li+/Li has been determined to play critical roles for capacity.<ref name=":02" /> The variety of methods of formations is also a factor of the low costs. However, issues with cycle stability and [[Chemical kinetics|kinetics]] have been limiting the progress of utilizing covellite in mainstream lithium batteries until future developments in its research.<ref name=":02" />

=== Nanostructures ===
The [[electron mobility]] and free hole density characteristics of covellite makes it an attractive choice for [[Nanostructure|nanoplatelets]] and nanocrystals because they provide the structures the ability to vary in size.<ref name=":03">{{Cite journal|last1=Liu|first1=Yang|last2=Zhang|first2=Hanguang|last3=Behara|first3=Pavan Kumar|last4=Wang|first4=Xiaoyu|last5=Zhu|first5=Dewei|last6=Ding|first6=Shuo|last7=Ganesh|first7=Sai Prasad|last8=Dupuis|first8=Michel|last9=Wu|first9=Gang|date=2018-11-19|title=Synthesis and Anisotropic Electrocatalytic Activity of Covellite Nanoplatelets with Fixed Thickness and Tunable Diameter|journal=ACS Applied Materials & Interfaces|volume=10|issue=49|pages=42417–42426|doi=10.1021/acsami.8b15895|pmid=30451490|s2cid=206495105|issn=1944-8244}}</ref><ref name=":12">{{Cite journal|last1=Liu|first1=Maixian|last2=Xue|first2=Xiaozheng|last3=Ghosh|first3=Chayanjit|last4=Liu|first4=Xin|last5=Liu|first5=Yang|last6=Furlani|first6=Edward P.|last7=Swihart|first7=Mark T.|last8=Prasad|first8=Paras N.|date=2015-04-03|title=Room-Temperature Synthesis of Covellite Nanoplatelets with Broadly Tunable Localized Surface Plasmon Resonance|journal=Chemistry of Materials|volume=27|issue=7|pages=2584–2590|doi=10.1021/acs.chemmater.5b00270|issn=0897-4756}}</ref> However, this ability can be limited by the plate-like structure all copper sulfides possess.<ref name=":03" /> Its [[Anisotropy|anisotropic]] electrical conductivity has been experimentally proven to be greater within layers (i.e. perpendicular to c-axis).<ref name=":03" /> Researchers have shown that covellite nanoplatelets of approx. two&nbsp;nm thick, with one unit cell and two copper atoms layers, and diameters around 100&nbsp;nm are ideal dimensions for [[electrocatalyst]]s in [[oxygen reduction reaction]]s (ORR).<ref name=":03" /> The basal planes experience preferential oxygen adsorption and larger surface area facilitates electron transfer.<ref name=":03" /> In contrast, with ambient conditions, nanoplatelets of dimensions of four&nbsp;nm width and greater than 30&nbsp;nm diameter have been experimentally synthesized with less cost and energy.<ref name=":12" /> Conversely, [[localized surface plasmon resonance]]s observed in covellite [[nanoparticle]]s have recently been linked to the [[stoichiometry]]-dependent [[band gap]] key for nanocrystals.<ref name=":2">{{Cite journal|last1=Xie|first1=Yi|last2=Riedinger|first2=Andreas|last3=Prato|first3=Mirko|last4=Casu|first4=Alberto|last5=Genovese|first5=Alessandro|last6=Guardia|first6=Pablo|last7=Sottini|first7=Silvia|last8=Sangregorio|first8=Claudio|last9=Miszta|first9=Karol|date=2013-11-06|title=Copper Sulfide Nanocrystals with Tunable Composition by Reduction of Covellite Nanocrystals with Cu+ Ions|journal=Journal of the American Chemical Society|volume=135|issue=46|pages=17630–17637|doi=10.1021/ja409754v|pmid=24128337|issn=0002-7863}}</ref><ref>{{Cite journal|last1=Xie|first1=Yi|last2=Bertoni|first2=Giovanni|last3=Riedinger|first3=Andreas|last4=Sathya|first4=Ayyappan|last5=Prato|first5=Mirko|last6=Marras|first6=Sergio|last7=Tu|first7=Renyong|last8=Pellegrino|first8=Teresa|last9=Manna|first9=Liberato|date=2015-10-29|title=Nanoscale Transformations in Covellite (CuS) Nanocrystals in the Presence of Divalent Metal Cations in a Mild Reducing Environment|journal=Chemistry of Materials|volume=27|issue=21|pages=7531–7537|doi=10.1021/acs.chemmater.5b03892|pmid=26617434|issn=0897-4756|pmc=4652895}}</ref> Thus, future chemical sensing devices, electronics, and others instruments are being explored with the use of nanostructures with covellite CuS.<ref name=":03" /><ref name=":2" />

==See also==

*[[List of minerals]]
*[[List of minerals named after people]]

== References ==
{{Reflist|2}}
*
{{commons category|Covellite}}
*

[[Category:Copper ores]]
[[Category:Sulfide minerals]]
[[Category:Hexagonal minerals]]
[[Category:Minerals in space group 194]]
[[Category:Minerals described in 1832]]