Covellite

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Covellite
Covellite-252597.jpg
General
Category Sulfide mineral
Formula
(repeating unit)		CuS (copper monosulfide)
IMA symbol Cv [1]
Strunz classification 2.CA.05a
Dana classification 02.08.12.01
Crystal system Hexagonal
Crystal class Dihexagonal dipyramidal (6/mmm)
H–M Symbol (6/m 2/m 2/m)
Space group P63/mmc
Unit cell a = 3.7938 Å, c = 16.341 Å; Z = 6
Identification
ColorIndigo-blue or darker, commonly highly iridescent, brass-yellow to deep red
Crystal habit Thin platy hexagonal crystals and rosettes also massive to granular.
Cleavage Perfect on {0001}
Tenacity Flexible
Mohs scale hardness1.5–2
Luster Submetallic, inclining to resinous to dull
Streak Lead gray
Diaphaneity Opaque
Specific gravity 4.6–4.8
Optical propertiesUniaxial (+)
Refractive index nω = 1.450 nε = 2.620
Pleochroism Marked, deep blue to pale blue
Fusibility 2.5
Other characteristicsMicaceous cleavage
References [2] [3] [4]
Covellite (gray) replacing and embaying chalcopyrite (light), polished section from Horn Silver Mine, San Francisco Mining District, Utah. Enlarged to 210 diameters. Cp--Covellite.jpg
Covellite (gray) replacing and embaying chalcopyrite (light), polished section from Horn Silver Mine, San Francisco Mining District, Utah. Enlarged to 210 diameters.

Covellite (also known as covelline) is a rare copper sulfide mineral with the formula CuS. [4] 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. [4]

Contents

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. [5] The first records are from Mount Vesuvius, formally named in 1832 after N. Covelli. [4]

Composition

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. [6] 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. [7] 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. [7] In contrast to the oxide CuO, the material is not a magnetic semiconductor but a metallic conductor with weak Pauli-paramagnetism. [8] 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. [7] The other 1/3 remains unpaired and together with Cu atoms forms hexagonal layers reminiscent of the boron nitride (graphite structure). [7] Thus, a description Cu+3S−S22− 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+3S2−S2− with a mixed sulfur oxidation state -2 and -1/2 is more appropriate. Despite the extended formula of Cu+3S2−S2− from researchers in 1976 and 1993, others have come up with variations, such as Cu+4Cu2+2(S2)2S2. [9] [10]

Structure

For a copper sulfide, covellite has a complicated lamellar structure, with alternating layers of CuS and Cu2S2 with copper atoms of trigonal planar (uncommon) and tetrahedral coordination respectively. [10] The layers are connected by S-S bonds (based on Van der Waals forces) known as S2 dimers. [10] The Cu2S2 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}. [7] The conductivity is greater across layers due to the partially filled 3p orbitals, facilitating electron mobility. [10]

Formation

A microscopic picture of covellite Covellite and Pyrite (V).jpg
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. [11] 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. [8]

Synthetic

Covellite's unique crystal structure is related to its complex oxidative formation conditions, as seen when attempting to synthesize covellite. [12] [13] Its formation also depends on the state and history of the associated sulfides it was derived from. Experimental evidence shows ammonium metavanadate (NH4VO3) to be a potentially important catalyst for covellite's solid state transformation from other copper sulfides. [13] Researchers discovered that covellite can also be produced in the lab under anaerobic conditions by sulfate reducing bacteria at a variety of temperatures. [14] 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. [14] 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. [12]

Occurrence

Covellite from the Black Forest, Germany Covellin - Grube Clara.jpg
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. [4] 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. [4] As a secondary mineral, covellite also forms as descending surface water in the supergene enrichment zone oxidizes and redeposits covellite on hypogene sulfides (pyrite and chalcopyrite) at the same locality. [4] An unusual occurrence of covellite was found replacing organic debris in the red beds of New Mexico. [15]

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. [4] His studies of its lava led to the discovery of several unknown minerals including covellite. [4]

Applications

Superconductors

Covellite was the first identified naturally occurring superconductor. [16] The framework of CuS3 /CuS2 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. [17] [18] Uses of covellite CuS superconductivity research can be seen in lithium batteries’ cathodes, ammonium gas sensors, and solar electric devices with metal chalcogenide thin films. [19] [20] [21]

Lithium ion batteries

Research into alternate cathode material for lithium batteries often examines the complex variations in stoichiometry and tetrahedron layered structure of copper sulfides. [22] Advantages include limited toxicity and low costs. [23] The high electrical conductivity of covellite (10−3 S cm−1) and a high theoretical capacity (560 mAh g−1) with flat discharge curves when cycled versus Li+/Li has been determined to play critical roles for capacity. [23] The variety of methods of formations is also a factor of the low costs. However, issues with cycle stability and kinetics have been limiting the progress of utilizing covellite in mainstream lithium batteries until future developments in its research. [23]

Nanostructures

The electron mobility and free hole density characteristics of covellite makes it an attractive choice for nanoplatelets and nanocrystals because they provide the structures the ability to vary in size. [24] [25] However, this ability can be limited by the plate-like structure all copper sulfides possess. [24] Its anisotropic electrical conductivity has been experimentally proven to be greater within layers (i.e. perpendicular to c-axis). [24] Researchers have shown that covellite nanoplatelets of approx. two nm thick, with one unit cell and two copper atoms layers, and diameters around 100 nm are ideal dimensions for electrocatalysts in oxygen reduction reactions (ORR). [24] The basal planes experience preferential oxygen adsorption and larger surface area facilitates electron transfer. [24] In contrast, with ambient conditions, nanoplatelets of dimensions of four nm width and greater than 30 nm diameter have been experimentally synthesized with less cost and energy. [25] Conversely, localized surface plasmon resonances observed in covellite nanoparticles have recently been linked to the stoichiometry-dependent band gap key for nanocrystals. [26] [27] Thus, future chemical sensing devices, electronics, and others instruments are being explored with the use of nanostructures with covellite CuS. [24] [26]

See also

Related Research Articles

Bioleaching is the extraction or liberation of metals from their ores through the use of living organisms. Bioleaching is one of several applications within biohydrometallurgy and several methods are used to treat ores or concentrates containing copper, zinc, lead, arsenic, antimony, nickel, molybdenum, gold, silver, and cobalt.

<span class="mw-page-title-main">Pyrite</span> Iron (II) disulfide mineral

The mineral pyrite ( PY-ryte), or iron pyrite, also known as fool's gold, is an iron sulfide with the chemical formula FeS2 (iron (II) disulfide). Pyrite is the most abundant sulfide mineral.

<span class="mw-page-title-main">Phosphor</span> Luminescent substance

A phosphor is a substance that exhibits the phenomenon of luminescence; it emits light when exposed to some type of radiant energy. The term is used both for fluorescent or phosphorescent substances which glow on exposure to ultraviolet or visible light, and cathodoluminescent substances which glow when struck by an electron beam in a cathode-ray tube.

<span class="mw-page-title-main">Chalcopyrite</span> Copper iron sulfide mineral

Chalcopyrite ( KAL-kə-PY-ryte, -⁠koh-) is a copper iron sulfide mineral and the most abundant copper ore mineral. It has the chemical formula CuFeS2 and crystallizes in the tetragonal system. It has a brassy to golden yellow color and a hardness of 3.5 to 4 on the Mohs scale. Its streak is diagnostic as green-tinged black.

<span class="mw-page-title-main">Sphalerite</span> Zinc-iron sulfide mineral

Sphalerite is a sulfide mineral with the chemical formula (Zn, Fe)S. It is the most important ore of zinc. Sphalerite is found in a variety of deposit types, but it is primarily in sedimentary exhalative, Mississippi-Valley type, and volcanogenic massive sulfide deposits. It is found in association with galena, chalcopyrite, pyrite, calcite, dolomite, quartz, rhodochrosite, and fluorite.

<span class="mw-page-title-main">Molybdenum disulfide</span> Chemical compound

Molybdenum disulfide is an inorganic compound composed of molybdenum and sulfur. Its chemical formula is MoS
2.

<span class="mw-page-title-main">Bornite</span> Sulfide mineral

Bornite, also known as peacock ore, is a sulfide mineral with chemical composition Cu5FeS4 that crystallizes in the orthorhombic system (pseudo-cubic).

<span class="mw-page-title-main">Chalcogenide</span>

A chalcogenide is a chemical compound consisting of at least one chalcogen anion and at least one more electropositive element. Although all group 16 elements of the periodic table are defined as chalcogens, the term chalcogenide is more commonly reserved for sulfides, selenides, tellurides, and polonides, rather than oxides. Many metal ores exist as chalcogenides. Photoconductive chalcogenide glasses are used in xerography. Some pigments and catalysts are also based on chalcogenides. The metal dichalcogenide MoS2 is a common solid lubricant.

<span class="mw-page-title-main">Copper monosulfide</span> Chemical compound

Copper monosulfide is a chemical compound of copper and sulfur. It was initially thought to occur in nature as the dark indigo blue mineral covellite. However, it was later shown to be rather a cuprous compound, formula Cu+3S(S2). CuS is a moderate conductor of electricity. A black colloidal precipitate of CuS is formed when hydrogen sulfide, H2S, is bubbled through solutions of Cu(II) salts. It is one of a number of binary compounds of copper and sulfur (see copper sulfide for an overview of this subject), and has attracted interest because of its potential uses in catalysis and photovoltaics.

<span class="mw-page-title-main">Djurleite</span> Copper sulfide mineral

Djurleite is a copper sulfide mineral of secondary origin with formula Cu31S16 that crystallizes with monoclinic-prismatic symmetry. It is typically massive in form, but does at times develop thin tabular to prismatic crystals. It occurs with other supergene minerals such as chalcocite, covellite and digenite in the enriched zone of copper orebodies. It is a member of the chalcocite group, and very similar to chalcocite, Cu2S, in its composition and properties, but the two minerals can be distinguished from each other by x-ray powder diffraction. Intergrowths and transformations between djurleite, digenite and chalcocite are common. Many of the reported associations of digenite and djurleite, however, identified by powder diffraction, could be anilite and djurleite, as anilite transforms to digenite during grinding.

Molybdenum dioxide is the chemical compound with the formula MoO2. It is a violet-colored solid and is a metallic conductor. The mineralogical form of this compound is called tugarinovite, and is only very rarely found. The discovery and early studies of molybdenum dioxide date back to the late 18th and early 19th centuries. One of the notable figures in the history of molybdenum dioxide is the Hungarian chemist Jakob Joseph Winterl (1732–1809). Winterl, who was a professor of chemistry and botany at the University of Budapest, made significant contributions to the understanding of molybdenum compounds. In 1787, he proposed that copper was a compound of nickel, molybdenum, silica, and a volatile substance, showcasing his interest in molybdenum chemistry.

<span class="mw-page-title-main">Carrollite</span> Mineral

Carrollite, CuCo2S4, is a sulfide of copper and cobalt, often with substantial substitution of nickel for the metal ions, and a member of the linnaeite group. It is named after the type locality in Carroll County, Maryland, US, at the Patapsco mine, Sykesville.

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.

<span class="mw-page-title-main">Cubanite</span> Copper iron sulfide mineral

Cubanite is a copper iron sulfide mineral that commonly occurs as a minor alteration mineral in magmatic sulfide deposits. It has the chemical formula CuFe2S3 and when found, it has a bronze to brass-yellow appearance. On the Mohs hardness scale, cubanite falls between 3.5 and 4 and has a orthorhombic crystal system. Cubanite is chemically similar to chalcopyrite; however, it is the less common copper iron sulfide mineral due to crystallization requirements.

<span class="mw-page-title-main">Titanium disulfide</span> Inorganic chemical compound

Titanium disulfide is an inorganic compound with the formula TiS2. A golden yellow solid with high electrical conductivity, it belongs to a group of compounds called transition metal dichalcogenides, which consist of the stoichiometry ME2. TiS2 has been employed as a cathode material in rechargeable batteries.

<span class="mw-page-title-main">Delafossite</span> Copper iron oxide mineral

Delafossite is a copper iron oxide mineral with formula CuFeO2 or Cu1+Fe3+O2. It is a member of the delafossite mineral group, which has the general formula ABO2, a group characterized by sheets of linearly coordinated A cations stacked between edge-shared octahedral layers (BO6). Delafossite, along with other minerals of the ABO2 group, is known for its wide range of electrical properties, its conductivity varying from insulating to metallic. Delafossite is usually a secondary mineral that crystallizes in association with oxidized copper and rarely occurs as a primary mineral.

<span class="mw-page-title-main">NASICON</span> Class of solid materials

NASICON is an acronym for sodium (Na) super ionic conductor, which usually refers to a family of solids with the chemical formula Na1+xZr2SixP3−xO12, 0 < x < 3. In a broader sense, it is also used for similar compounds where Na, Zr and/or Si are replaced by isovalent elements. NASICON compounds have high ionic conductivities, on the order of 10−3 S/cm, which rival those of liquid electrolytes. They are caused by hopping of Na ions among interstitial sites of the NASICON crystal lattice.

Copper selenide is an inorganic binary compound between copper and selenium. The chemical formula depends on the ratio between the two elements, such as CuSe or Cu2Se.

Quantum dots (QDs) are semiconductor nanoparticles with a size less than 10 nm. They exhibited size-dependent properties especially in the optical absorption and the photoluminescence (PL). Typically, the fluorescence emission peak of the QDs can be tuned by changing their diameters. So far, QDs were consisted of different group elements such as CdTe, CdSe, CdS in the II-VI category, InP or InAs in the III-V category, CuInS2 or AgInS2 in the I–III–VI2 category, and PbSe/PbS in the IV-VI category. These QDs are promising candidates as fluorescent labels in various biological applications such as bioimaging, biosensing and drug delivery.

<span class="mw-page-title-main">Rhenium disulfide</span> Chemical compound

Rhenium disulfide is an inorganic compound of rhenium and sulfur with the formula ReS2. It has a layered structure where atoms are strongly bonded within each layer. The layers are held together by weak Van der Waals bonds, and can be easily peeled off from the bulk material.

References

  1. ↑ Warr, L.N. (2021). "IMA–CNMNC approved mineral symbols". Mineralogical Magazine. 85 (3): 291–320. Bibcode:2021MinM...85..291W. doi: 10.1180/mgm.2021.43 . S2CID   235729616.
  2. ↑ Handbook of Mineralogy
  3. ↑ Webmineral data
  4. 1 2 3 4 5 6 7 8 9 Mindat.org
  5. ↑ Q. Ashton Acton (2012). Chlorine Compounds-Advances in Research and Application. ScholarlyMedia LLC. ISBN   9781481600040. OCLC   1024280169.
  6. ↑ Putnis, A.; Grace, J.; Cameron, W. E. (1977). "Blaubleibender covellite and its relationship to normal covellite". Contributions to Mineralogy and Petrology. 60 (2): 209–217. Bibcode:1977CoMP...60..209P. doi:10.1007/bf00372282. ISSN   0010-7999. S2CID   95661500.
  7. 1 2 3 4 5 Evans, Howard T.; Konnert, Judith A. (1976). "Crystal structure refinement of covellite". American Mineralogist. 61: 996–1000.
  8. 1 2 Warner, Terence E. (2013). Synthesis, properties and mineralogy of important inorganic materials. Wiley. ISBN   9780470976234. OCLC   865009780.
  9. ↑ Goble, Ronald J. (1985). The relationship between crystal structure, bonding and cell dimensions in the copper sulfides : supplementary unpublished material. OCLC   45557917.
  10. 1 2 3 4 Liang, W.; Whangbo, M.-H. (February 1993). "Conductivity anisotropy and structural phase transition in Covellite CuS". Solid State Communications. 85 (5): 405–408. Bibcode:1993SSCom..85..405L. doi:10.1016/0038-1098(93)90689-k. ISSN   0038-1098.
  11. ↑ Majzlan, Juraj; Kiefer, Stefan; Herrmann, Julia; Števko, Martin; Sejkora, Jiří; Chovan, Martin; Lánczos, Tomáš; Lazarov, Marina; Gerdes, Axel (June 2018). "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". Chemical Geology. 488: 1–20. Bibcode:2018ChGeo.488....1M. doi:10.1016/j.chemgeo.2018.04.021. ISSN   0009-2541. S2CID   135253715.
  12. 1 2 Simonescu, C.M., Teodorescu, V.S., Carp, O., Patron, L. and Capatina, C. (2007). "Thermal behaviour of CuS (covellite) obtained from copper–thiosulfate system". Journal of Thermal Analysis and Calorimetry . 88 (1): 71–76. doi:10.1007/s10973-006-8079-z. S2CID   94104147.{{cite journal}}: CS1 maint: multiple names: authors list (link)
  13. 1 2 Ghezelbash, Ali; Korgel, Brian A. (October 2005). "Nickel Sulfide and Copper Sulfide Nanocrystal Synthesis and Polymorphism". Langmuir. 21 (21): 9451–9456. doi:10.1021/la051196p. ISSN   0743-7463. PMID   16207021.
  14. 1 2 Gramp, J.P.; Sasaki, K.; Bigham, J.M.; Karnachuck, O.V.; Tuovinen, O.H. (2006). "Formation of Covellite (CuS) Under Biological Sulfate-Reducing Conditions". Geomicrobiology Journal . 23 (8): 613–619. doi:10.1080/01490450600964383. S2CID   95152748.
  15. ↑ Emmons, W. H., The Enrichment of Ore Deposits, Bulletin 625, United States Geological Survey, 1917, p. 193
  16. ↑ Benedetto, F.D.; Borgheresi, M.; Caneschi, A.; Chastanet, G.; Cipriani, C.; Gatteschi, D.; Pratesi, G.; Romanelli, M.; Sessoli, R. (2006). "First evidence of natural superconductivity". European Journal of Mineralogy . 18 (3): 283–287. Bibcode:2006EJMin..18..283D. doi:10.1127/0935-1221/2006/0018-0283.
  17. ↑ Chunyan Wu; Shu-Hong Yu; Markus Antoniette (2006). "Complex Concaved Cuboctahedrons of Copper Sulfide Crystals with Highly Geometrical Symmetry Created by a Solution Process". Chemistry of Materials . 18 (16): 3599–3601. doi:10.1021/cm060956u.
  18. ↑ Nava, Dora; Gonzalez, I; et al. (2006). "Electrochemical characterization of chemical species formed during the electrochemical treatment of chalcopyrite in sulfuric acid". Electrochimica Acta . 51 (25): 5295–5303. doi:10.1016/j.electacta.2006.02.005.
  19. ↑ Chung, J.-S.; Sohn, H.-J. (June 2002). "Electrochemical behaviors of CuS as a cathode material for lithium secondary batteries". Journal of Power Sources. 108 (1–2): 226–231. Bibcode:2002JPS...108..226C. doi:10.1016/s0378-7753(02)00024-1. ISSN   0378-7753.
  20. ↑ Sagade, Abhay A.; Sharma, Ramphal (July 2008). "Copper sulphide (CuxS) as an ammonia gas sensor working at room temperature". Sensors and Actuators B: Chemical. 133 (1): 135–143. doi:10.1016/j.snb.2008.02.015. ISSN   0925-4005.
  21. ↑ Mane, R. S.; Lokhande, C. D. (2010-06-03). "ChemInform Abstract: Chemical Deposition Method for Metal Chalcogenide Thin Films". ChemInform. 31 (34): no. doi:10.1002/chin.200034236. ISSN   0931-7597.
  22. ↑ Foley, Sarah; Geaney, Hugh; Bree, Gerard; Stokes, Killian; Connolly, Sinead; Zaworotko, Michael J.; Ryan, Kevin M. (2018-03-24). "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". Advanced Functional Materials. 28 (19): 1800587. doi:10.1002/adfm.201800587. ISSN   1616-301X. S2CID   104176144.
  23. 1 2 3 Zhou, Mingjiong; Peng, Na; Liu, Zhen; Xi, Yun; He, Huiqiu; Xia, Yonggao; Liu, Zhaoping; Okada, Shigeto (February 2016). "Synthesis of sub-10 nm copper sulphide rods as high-performance anode for long-cycle life Li-ion batteries". Journal of Power Sources. 306: 408–412. Bibcode:2016JPS...306..408Z. doi:10.1016/j.jpowsour.2015.12.048. ISSN   0378-7753.
  24. 1 2 3 4 5 6 Liu, Yang; Zhang, Hanguang; Behara, Pavan Kumar; Wang, Xiaoyu; Zhu, Dewei; Ding, Shuo; Ganesh, Sai Prasad; Dupuis, Michel; Wu, Gang (2018-11-19). "Synthesis and Anisotropic Electrocatalytic Activity of Covellite Nanoplatelets with Fixed Thickness and Tunable Diameter". ACS Applied Materials & Interfaces. 10 (49): 42417–42426. doi:10.1021/acsami.8b15895. ISSN   1944-8244. PMID   30451490. S2CID   206495105.
  25. 1 2 Liu, Maixian; Xue, Xiaozheng; Ghosh, Chayanjit; Liu, Xin; Liu, Yang; Furlani, Edward P.; Swihart, Mark T.; Prasad, Paras N. (2015-04-03). "Room-Temperature Synthesis of Covellite Nanoplatelets with Broadly Tunable Localized Surface Plasmon Resonance". Chemistry of Materials. 27 (7): 2584–2590. doi:10.1021/acs.chemmater.5b00270. ISSN   0897-4756.
  26. 1 2 Xie, Yi; Riedinger, Andreas; Prato, Mirko; Casu, Alberto; Genovese, Alessandro; Guardia, Pablo; Sottini, Silvia; Sangregorio, Claudio; Miszta, Karol (2013-11-06). "Copper Sulfide Nanocrystals with Tunable Composition by Reduction of Covellite Nanocrystals with Cu+ Ions". Journal of the American Chemical Society. 135 (46): 17630–17637. doi:10.1021/ja409754v. ISSN   0002-7863. PMID   24128337.
  27. ↑ Xie, Yi; Bertoni, Giovanni; Riedinger, Andreas; Sathya, Ayyappan; Prato, Mirko; Marras, Sergio; Tu, Renyong; Pellegrino, Teresa; Manna, Liberato (2015-10-29). "Nanoscale Transformations in Covellite (CuS) Nanocrystals in the Presence of Divalent Metal Cations in a Mild Reducing Environment". Chemistry of Materials. 27 (21): 7531–7537. doi:10.1021/acs.chemmater.5b03892. ISSN   0897-4756. PMC   4652895 . PMID   26617434.
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