Digenite is a
copper 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: Cu
9S
5. 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 ...
of 2.5 to 3 and a
specific gravity 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.
...
,
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 ...
,
djurleite,
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 Fe S2 (iron (II) disulfide). Pyrite is the most abundant sulfide mineral.
Pyrite's metallic luster and pale brass-yellow hue giv ...
. The
type locality is
Sangerhausen,
Thuringia,
Germany, in copper slate deposits.
[
]
Occurrence
Digenite occurs in the transitional zone of supergene oxidation 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
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.
...
further up in the weathering profile, and is a minor weathering product of primary 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 ...
. 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, 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 ''digenus'' meaning of two origins in reference to its close resemblance 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.
...
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 series between high digenite and berzelianite Cu2−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 Cu7.2−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 Cu1.8S.][ 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 Cu1.8S.
]
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