Digenite

Digenite
Digenite from the East Colusa Mine, Butte, Montana, US. Specimen size = 4.3 cm
General
Category	Sulfide mineral
Formula (repeating unit)	Cu9S5
IMA symbol	Dg[1]
Strunz classification	2.BA.05e
Dana classification	02.04.07.03
Crystal system	Trigonal
Crystal class	Hexagonal scalenohedral (3m) H-M symbol: (3 2/m)
Space group	R3m
Identification
Formula mass	146.45 g/mol
Color	Blue to black
Crystal habit	Pseudocubic crystals are rare, usually as intergrowths with other copper sulfides
Cleavage	{111} (observed in synthetic material)
Fracture	Conchoidal
Tenacity	Brittle
Mohs scale hardness	2.5 to 3
Luster	Submetallic to metallic
Streak	Black
Diaphaneity	Opaque
Specific gravity	5.5 to 5.7 observed, 5.628 calculated
Optical properties	Reflectivity: 21.6 at 540 nm
Other characteristics	Distinctly blue in polished sections
References	[2][3][4][5]

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.^[2]