Digenite is a

copper Copper is a chemical element with the symbol Cu (from la, cuprum) 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 pinkis ...

sulfide Sulfide (British English also sulphide) 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 chemical compounds lar ...

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 various minerals through the ability of harder material to scratch softer material. The scale was introduced in 1812 by th ...

of 2.5 to 3 and a

specific gravity Relative density, or specific gravity, is the ratio of the density (mass of a unit volume) of a substance to the density of a given reference material. Specific gravity for liquids is nearly always measured with respect to water (molecule), wa ...

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 Chalcocite (), copper(I) sulfide (Cu2S), is an important copper ore mineral. It is opaque and dark gray to black, with a metallic luster. It has a hardness of 2.5–3 on the Mohs scale. It is a sulfide with a monoclinic crystal system. The ...

covellite Covellite (also known as covelline) is a rare copper sulfide mineral with the formula CuS. 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 t ...

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 oth ...

bornite Bornite, also known as peacock ore, is a sulfide mineral with chemical composition Cu5 Fe S4 that crystallizes in the orthorhombic system (pseudo-cubic). Appearance Bornite has a brown to copper-red color on fresh surfaces that tarnishes to v ...

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 hardness of 3.5 to 4 on the Mo ...

and

pyrite The mineral pyrite (), or iron pyrite, also known as fool's gold, is an iron sulfide with the chemical formula Iron, FeSulfur, S2 (iron (II) disulfide). Pyrite is the most abundant sulfide mineral. Pyrite's metallic Luster (mineralogy), lust ...

. The type locality is

Sangerhausen Sangerhausen () is a town in Saxony-Anhalt, central Germany, capital of the district of Mansfeld-Südharz. It is situated southeast of the Harz, approx. east of Nordhausen, and west of Halle (Saale). About 26,000 people live in Sangerhausen ( ...

Thuringia Thuringia (; german: Thüringen ), officially the Free State of Thuringia ( ), is a state of central Germany, covering , the sixth smallest of the sixteen German states. It has a population of about 2.1 million. Erfurt is the capital and larg ...

Germany Germany,, officially the Federal Republic of Germany, is a country in Central Europe. It is the second most populous country in Europe after Russia, and the most populous member state of the European Union. Germany is situated betwe ...

, in copper slate deposits.

Occurrence

Digenite occurs in the transitional zone of supergene

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

of primary sulfide ore deposits, at the interface between the upper and lower

saprolite Saprolite is a chemically weathered rock. Saprolites form in the lower zones of soil profiles and represent deep weathering of the bedrock surface. In most outcrops its color comes from ferric compounds. Deeply weathered profiles are widespread o ...

ore zones. It is rarely an important mineral for copper ores, as it is more usually replaced by

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,

Western Australia Western Australia (commonly abbreviated as WA) is a state of Australia occupying the western percent of the land area of Australia excluding external territories. It is bounded by the Indian Ocean to the north and west, the Southern Ocean to th ...

, 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

Greek Greek may refer to: Greece Anything of, from, or related to Greece, a country in Southern Europe: *Greeks, an ethnic group. *Greek language, a branch of the Indo-European language family. **Proto-Greek language, the assumed last common ancestor ...

''digenus'' meaning of two origins in reference to its close resemblance with

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 homogenous mixture of two different kinds of atoms in solid state and have a single crystal structure. Many examples can be found in metallurgy, geology, and solid-state chemistry. The word ...

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