Djurleite

Djurleite
Djurleite pseudomorph after pyrite from New Mexico, specimen size 2.4 cm
General
Category	Copper sulfide
Formula (repeating unit)	Cu31S16
Strunz classification	2.BA.05b
Dana classification	2.4.7.2
Crystal system	Monoclinic
Crystal class	Prismatic (2/m) (same H-M symbol)
Space group	P21/n
Unit cell	a = 26.897, b = 15.745 c = 13.565 [Å]; β = 90.13°; Z = 8
Identification
Formula mass	2483 g/mol
Color	Grey, blue-black or black
Crystal habit	Crystals are short prismatic and thick tabular, also massive and compact
Twinning	Pseudohexagonal twins are common, twin axis [100].
Cleavage	None
Fracture	Conchoidal
Tenacity	Brittle
Mohs scale hardness	2½ to 3
Luster	Submetallic to metallic
Streak	Black
Diaphaneity	Opaque
Specific gravity	5.63
References

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 and digenite in the enriched zone of copper orebodies. It is a member of the chalcocite group, and very similar to chalcocite, Cu₂S, in its composition and properties, but the two minerals can be distinguished from each other by x-ray powder diffraction. Intergrowths and transformations between djurleite, digenite and chalcocite are common. Many of the reported associations of digenite and djurleite, however, identified by powder diffraction, could be anilite and djurleite, as anilite transforms to digenite during grinding.

Djurleite was named for the Swedish chemist Seved Djurle (1928–2000), from the University of Uppsala, Sweden, who first synthesized the mineral in 1958, prior to its discovery in nature. The natural material was first described in 1962 by E H Roseboom Jr, of the US Geological Survey, from occurrences at the type locality, Barranca del Cobre, Chihuahua, Mexico.

The chalcocite group is a group of closely related copper sulfides, with the formulae:

Djurleite has a monoclinic structure with a large unit cell containing 248 copper and 128 sulfur atoms. The formula is Cu₃₁S₁₆, molar mass 2483 g, and there are 8 formula units per unit cell (Z = 8).