Digenite
Encyclopedia
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 fracture. It has a Mohs hardness 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
, covellite
, djurleite
, bornite
, chalcopyrite
and pyrite
. The type locality
is Sangerhausen
, Thuringia
, Germany
, in copper slate deposits.
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
further up in the weathering profile, and is a minor weathering product of primary chalcopyrite
. Natural digenite always contains a small amount of iron and is considered to be stable only in the Cu-Fe-S system.
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
and covellite.
s of digenite, high, metastable and low. There is a complete solid solution
series between high digenite and berzelianite Cu2-xSe (x~0.12).
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 Fdm and a=27.85 Å, ie the same as the apparent isometric symmetry of the metastable polymorph, Z=4 for formula Cu1.8S.
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...
sulfide
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 :...
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 of 2.5 to 3 and a specific gravity
Specific gravity
Specific gravity is the ratio of the density of a substance to the density of a reference substance. Apparent specific gravity is the ratio of the weight of a volume of the substance to the weight of an equal volume of the reference substance. The reference substance is nearly always water for...
of 5.6. It is found in copper sulfide deposits of both primary and 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...
occurrences. It is typically associated with and often intergrown with chalcocite
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....
, covellite
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...
, djurleite
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...
, bornite
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...
, chalcopyrite
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...
and pyrite
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...
. 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....
is Sangerhausen
Sangerhausen
Sangerhausen is a town in Saxony-Anhalt, Germany, capital of the district of Mansfeld-Südharz, without being part of it.It is situated southeast of the Harz, approx. 35 km east of Nordhausen, and 50 km west of Halle...
, Thuringia
Thuringia
The Free State of Thuringia is a state of Germany, located in the central part of the country.It has an area of and 2.29 million inhabitants, making it the sixth smallest by area and the fifth smallest by population of Germany's sixteen states....
, Germany
Germany
Germany , officially the Federal Republic of Germany , is a federal parliamentary republic in Europe. The country consists of 16 states while the capital and largest city is Berlin. Germany covers an area of 357,021 km2 and has a largely temperate seasonal climate...
, in copper slate deposits.
Occurrence
Digenite occurs in the transitional zone of supergeneSupergene (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...
oxidation of primary sulfide ore deposits, at the interface between the upper and lower saprolite
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...
ore zones. It is rarely an important mineral for copper ores, as it is more usually replaced by chalcocite
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....
further up in the weathering profile, and is a minor weathering product of primary chalcopyrite
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...
. Natural digenite always contains a small amount of iron and is considered to be stable only in the Cu-Fe-S system.
In the Deflector and Deflector West Cu-Au lode deposits of the Gullewa Greenstone Belt, Western Australia
Western Australia
Western Australia is a state of Australia, occupying the entire western third of the Australian continent. It is bounded by the Indian Ocean to the north and west, the Great Australian Bight and Indian Ocean to the south, the Northern Territory to the north-east and South Australia to the south-east...
, 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 language
Greek is an independent branch of the Indo-European family of languages. Native to the southern Balkans, it has the longest documented history of any Indo-European language, spanning 34 centuries of written records. Its writing system has been the Greek alphabet for the majority of its history;...
digenus meaning of two origins in reference to its close resemblance with chalcocite
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....
and covellite.
Polymorphs of Digenite
There are three polymorphPolymorphism (materials science)
Polymorphism in materials science is the ability of a solid material to exist in more than one form or crystal structure. Polymorphism can potentially be found in any crystalline material including polymers, minerals, and metals, and is related to allotropy, which refers to chemical elements...
s of digenite, high, metastable and low. There is a complete 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...
series between high digenite and berzelianite Cu2-xSe (x~0.12).
High digenite is stable above 73 °C, with space group Fmm and unit cell parameters a=5.57 Å
Ångström
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....
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 Fdm and a=27.85 Å, ie the same as the apparent isometric symmetry of the metastable polymorph, Z=4 for formula Cu1.8S.