Carrollite, CuCo2S4, is a sulfide
A sulfide is an anion of sulfur in its lowest oxidation state of 2-. Sulfide is also a slightly archaic term for thioethers, a common type of organosulfur compound that are well known for their bad odors.- Properties :...

 of copper
Copper is a chemical element with the symbol Cu and atomic number 29. It is a ductile metal with very high thermal and electrical conductivity. Pure copper is soft and malleable; an exposed surface has a reddish-orange tarnish...

 and cobalt
Cobalt is a chemical element with symbol Co and atomic number 27. It is found naturally only in chemically combined form. The free element, produced by reductive smelting, is a hard, lustrous, silver-gray metal....

, often with substantial substitution of nickel
Nickel is a chemical element with the chemical symbol Ni and atomic number 28. It is a silvery-white lustrous metal with a slight golden tinge. Nickel belongs to the transition metals and is hard and ductile...

 for the metal ions, and a member of the linnaeite
Linnaeite is a cobalt sulfide mineral with the composition Co+2Co+32S4 . It was discovered in 1845 in Västmanland, Sweden, and was named to honor Carl Linnaeus ....

 group. It is named after the type locality
Type locality (geology)
Type locality , also called type area or type locale, is the where a particular rock type, stratigraphic unit, fossil or mineral species is first identified....

 in Carroll County, Maryland
Carroll County, Maryland
Carroll County is a county located in the U.S. state of Maryland. In 2010, its population was 167,134. It was named for Charles Carroll of Carrollton , signer of the American Declaration of Independence. Its county seat is Westminster....

, USA, at the Patapsco mine, Finksburg, Sykesville.

Unit cell

Space group: Fd3m. Unit cell parameters = a = 9.48 Å
The angstrom or ångström, is a unit of length equal to 1/10,000,000,000 of a meter . Its symbol is the Swedish letter Å....

 , Z = 8. Unit cell volume: V = 851.97 Å³ (calculated from unit cell parameters).

Linnaeite group

The linnaeite group is a group of sulfides and selenides with the general formula AB2X4 in which X is sulfur
Sulfur or sulphur is the chemical element with atomic number 16. In the periodic table it is represented by the symbol S. It is an abundant, multivalent non-metal. Under normal conditions, sulfur atoms form cyclic octatomic molecules with chemical formula S8. Elemental sulfur is a bright yellow...

 or selenium
Selenium is a chemical element with atomic number 34, chemical symbol Se, and an atomic mass of 78.96. It is a nonmetal, whose properties are intermediate between those of adjacent chalcogen elements sulfur and tellurium...

, A is divalent
In chemistry, a divalent ion or molecule has a valence of two and thus can form two bonds with other ions or molecules. An older term for divalent is bivalent....

 Fe, Ni, Co or Cu and B is trivalent Co, Ni or, for daubreelite, Cr. The minerals are isometric
The term isometric comes from the Greek for "having equal measurement".isometric may mean:* Isometric projection , a method for the visual representation of three-dimensional objects in two dimensions; a form of orthographic projection, or more specifically, an axonometric projection.* Isometry and...

, space group
Space group
In mathematics and geometry, a space group is a symmetry group, usually for three dimensions, that divides space into discrete repeatable domains.In three dimensions, there are 219 unique types, or counted as 230 if chiral copies are considered distinct...

 Fd3m and isostructural with each other and with minerals of the spinel group.

The structure of the linnaeite group consists of a cubic close packed array of X (X is oxygen in the spinels and sulfur or selenium
Selenium is a chemical element with atomic number 34, chemical symbol Se, and an atomic mass of 78.96. It is a nonmetal, whose properties are intermediate between those of adjacent chalcogen elements sulfur and tellurium...

 in the linnaeite group). Within the array of Xs there are two types of interstices, one type tetrahedrally co-ordinated and one type octahedrally co-ordinated. One eighth of the tetrahedal sites A are typically occupied by 2+ cations, and half of the octahedral sites B by 3+ cations. Charnock et al confirmed that carrollite contains Cu wholly within the tetrahedral sites. Thus, the ideal formula one would expect for a spinel like carrollite is Cu2+Co3+2S2-4, but as in the case of copper sulfide
Copper sulfide
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....

s in general the oxidation state of the copper atom is 1+, not 2+. An assignement of valences as Cu+Co3+2S1.75-4 is more appropriate. This was confirmed in a study of 2009. The one missing electron per four sulfur atoms is delocalized leading to metallic conductivity and even superconductivity at very low temperatures, combined with a complicated magnetic behavior.

Solid solutions

A solid solution
Solid solution
A solid solution is a solid-state solution of one or more solutes in a solvent. Such a mixture is considered a solution rather than a compound when the crystal structure of the solvent remains unchanged by addition of the solutes, and when the mixture remains in a single homogeneous phase...

 results when one cation can substitute for another across an appreciable composition range. In carrollite Co2+ can substitute for Cu+ at the A sites, and when the substitution is complete the mineral formed is called linnaeite, Co2+Co3+2S4. This means that there is a solid solution series between carrollite and linnaeite. Also, Ni substitutes for both Co and Cu in the carrollite structure, giving a solid solution from carrollite to cuprian siegenite. Siegenite
Siegenite is a cobalt nickel sulfide mineral with formula: 3S4 . It was found at the Browns deposit, Batchelor, Northern Territory, Australia....

, Co2+Ni3+2S4, is itself a member of the solid solution series between linnaeite and polydymite
Polydymite, Ni2+Ni23+S4, is a supergene thiospinel sulfide mineral associated with the weathering of primary pentlandite nickel sulfide.Polydymite crystallises in the isometric system, with a hardness of 4.5 to 5.5 and a specific gravity of about 4, is dark violet gray to copper-red, often with...

, Ni2+Ni3+2S4. (Wagner and Cook found no evidence for solid solution between carrollite and fletcherite
Fletcherite is a rare thiospinel sulfide mineral with formula Cu2S4. It is an opaque metallic steel gray mineral which crystallizes in the Cubic crystal system...

, CuNi2S4).


Carrollite occurs in hydrothermal vein deposits associated with tetrahedrite
Tetrahedrite is a copper antimony sulfosalt mineral with formula: 12Sb4S13. It is the antimony endmember of the continuous solid solution series with arsenic bearing tennantite. Pure endmembers of the series are seldom if ever seen in nature. Of the two, the antimony rich phase is more common...

, chalcopyrite
Chalcopyrite is a copper iron sulfide mineral that crystallizes in the tetragonal system. It has the chemical composition CuFeS2. 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.On exposure to air, chalcopyrite...

, bornite
Bornite is a sulfide mineral with chemical composition Cu5FeS4 that crystallizes in the orthorhombic system .-Appearance:Bornite has a brown to copper-red color on fresh surfaces that tarnishes to various iridescent shades of blue to purple in places...

, digenite
Digenite is a copper sulfide mineral with formula: Cu9S5. Digenite is a black to dark blue opaque mineral that crystallizes with a trigonal - hexagonal scalenohedral structure. In habit it is usually massive, but does often show pseudo-cubic forms. It has poor to indistinct cleavage and a brittle...

, djurleite
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...

, chalcocite
Chalcocite, copper sulfide , is an important copper ore mineral. It is opaque, being colored dark-gray to black with a metallic luster. It has a hardness of 2½ - 3. It is a sulfide with an orthorhombic crystal system....

, pyrrhotite
Pyrrhotite is an unusual iron sulfide mineral with a variable iron content: FeS . The FeS endmember is known as troilite. Pyrrhotite is also called magnetic pyrite because the color is similar to pyrite and it is weakly magnetic...

, pyrite
The mineral pyrite, or iron pyrite, is an iron sulfide with the formula FeS2. This mineral's metallic luster and pale-to-normal, brass-yellow hue have earned it the nickname fool's gold because of its resemblance to gold...

, sphalerite
Sphalerite is a mineral that is the chief ore of zinc. It consists largely of zinc sulfide in crystalline form but almost always contains variable iron. When iron content is high it is an opaque black variety, marmatite. It is usually found in association with galena, pyrite, and other sulfides...

, millerite
Millerite is a nickel sulfide mineral, NiS. It is brassy in colour and has an acicular habit, often forming radiating masses and furry aggregates...

, gersdorffite
Gersdorffite is a nickel arsenic sulfide mineral with formula NiAsS. It crystallizes in the isometric system showing diploidal symmetry. It occurs as euhedral to massive opaque, metallic grey-black to silver white forms. Gersdorffite belongs to a solid solution series with cobaltite, CoAsS....

, ullmannite
Ullmannite is a nickel antimony sulfide mineral with formula: NiSbS. Considerable substitution occurs with cobalt and iron in the nickel site along with bismuth and arsenic in the antimony site...

, cobaltoan calcite
Calcite is a carbonate mineral and the most stable polymorph of calcium carbonate . The other polymorphs are the minerals aragonite and vaterite. Aragonite will change to calcite at 380-470°C, and vaterite is even less stable.-Properties:...

, and with linnaeite group members linnaeite, siegenite and polydymite.

Phase relations in the Cu-Co-S system have been investigated. At temperatures around 900 °C a chalcocite-digenite solid solution coexists with cobalt sulfides. With decreasing temperature, at 880 °C a carrollite-linnaeite solid solution develops, becoming more copper-rich on coling, with the carrollite composition at about 500 °C. Below 507 °C covellite
Covellite is a rare copper sulfide mineral with the formula CuS. This indigo blue mineral is ubiquitous in copper ores, it is found in limited abundance and is not an important ore of copper itself, although it is well known to mineral collectors.The mineral is associated with chalcocite in zones...

 is stable and coexists with copper-bearing cattierite
Cattierite is a mineral found in the Democratic Republic of Congo. It was discovered together with Vaesite by Johannes F. Vaes, a Belgian mineralologist and named after Felicien Cattier, Chairman of the Board, Union Miniere du Haut Katanga....

. Low chalcocite appears at 103 °C, djurleite appears at 93 °C, and digenite disappears and anilite appears around 70 °C.
There is some evidence for supergene
Supergene (geology)
In ore deposit geology, supergene processes or enrichment occur relatively near the surface. Supergene processes include the predominance of meteoric water circulation with concomitant oxidation and chemical weathering. The descending meteoric waters oxidize the primary sulfide ore minerals and...

replacement of an intermediate member of the linnaeite-carrollite series by djurleite.


Carrollite is found in Australia, Austria, Azerbaijan, Brazil, Bulgaria, Canada, Chile, China, the Czech Republic, the Democratic Republic of Congo, France, Germany, Japan, Morocco, Namibia, North Korea, Norway, Oman, Poland, Romania, Russia, Slovakia, Sweden, Switzerland, USA and Zambia.
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