Digenite is a

copper Copper is a chemical element; it has symbol Cu (from Latin ) and atomic number 29. It is a soft, malleable, and ductile metal with very high thermal and electrical conductivity. A freshly exposed surface of pure copper has a pinkish-orang ...

sulfide Sulfide (also sulphide in British English) is an inorganic anion of sulfur with the chemical formula S2− or a compound containing one or more S2− ions. Solutions of sulfide salts are corrosive. ''Sulfide'' also refers to large families o ...

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 fracture. It has a

Mohs hardness The Mohs scale ( ) of mineral hardness is a qualitative ordinal scale, from 1 to 10, characterizing scratch resistance of mineral In geology and mineralogy, a mineral or mineral species is, broadly speaking, a solid substance with a fair ...

of 2.5 to 3 and a

specific gravity Relative density, also called specific gravity, is a dimensionless quantity defined as the ratio of the density (mass of a unit volume) of a substance to the density of a given reference material. Specific gravity for solids and liquids is nea ...

of 5.6. It is found in copper sulfide deposits of both primary and supergene occurrences. It is typically associated with and often intergrown with chalcocite, covellite, djurleite, bornite,

chalcopyrite Chalcopyrite ( ) 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 Mohs scale, hardness of 3.5 to 4 ...

and

pyrite The mineral pyrite ( ), or iron pyrite, also known as fool's gold, is an iron sulfide with the chemical formula Fe S2 (iron (II) disulfide). Pyrite is the most abundant sulfide mineral. Pyrite's metallic luster and pale brass-yellow hue ...

. The type locality is Sangerhausen,

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, in copper slate deposits.

Occurrence

Digenite occurs in the transitional zone of supergene

oxidation Redox ( , , reduction–oxidation or oxidation–reduction) is a type of chemical reaction in which the oxidation states of the reactants change. Oxidation is the loss of electrons or an increase in the oxidation state, while reduction is ...

of primary sulfide ore deposits, at the interface between the upper and lower saprolite ore zones. It is rarely an important mineral for copper ores, as it is more usually replaced by chalcocite further up in the weathering profile, and is a minor weathering product of primary

. Natural digenite always contains a small amount of iron and is considered to be stable only in the Cu-Fe-S system.American Mineralogist (1970) 55:106 In the Deflector and Deflector West Cu-Au lode deposits of the Gullewa Greenstone Belt,

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, digenite is an important constituent of the transitional Cu-Au ore. However, it is difficult to treat metallurgically and remains a refractory ore type. In this locality digenite is found with covellite, chalcocite and bornite. It was first described in 1844 from the type locality of Sangerhausen, Saxony-Anhalt, Germany. The name is from the

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''digenus'' meaning of two origins in reference to its close resemblance with chalcocite and covellite.

Polymorphs of digenite

There are three polymorphs of digenite, high, metastable and low.American Mineralogist (1963) 48:110 There is a complete

solid solution A solid solution, a term popularly used for metals, is a homogeneous mixture of two compounds in solid state and having a single crystal structure. Many examples can be found in metallurgy, geology, and solid-state chemistry. The word "solutio ...

series between high digenite and berzelianite Cu_2−xSe (x~0.12).Canadian Mineralogist (2008) 46: 219-231 High digenite is stable above 73 °C, with space group Fmm and unit cell parameters a = 5.57 Å and Z = 1 for formula Cu_7.2−xS₄. High digenite is isostructural with bornite Cu₅FeS₄. Metastable digenite forms on cooling from 73 °C. It appears to be isometric with space group Fdm and a = 27.85 Å. This symmetry, however, is due to twinning of fine domains with rhombohedral symmetry, trigonal -3m, point group R-3m, a = 3.92 Å, c = 48 Å, Z = 15 for formula Cu_1.8S. Metastable digenite changes with time to stable low temperature digenite or a mixture of anilite Cu₇S₄ and djurleite Cu₃₁S₁₆. Low digenite is isometric, space group Fd{{overline, 3m and a = 27.85 Å, i.e. the same as the apparent isometric symmetry of the metastable polymorph, Z=4 for formula Cu_1.8S.

References

* Palache, C., H. Berman, and C. Frondel (1944) ''Dana’s system of mineralogy'', (7th edition), v. I, pp. 180–182. Sulfide minerals Copper ores Trigonal minerals Minerals in space group 166