Duftite

Duftite
Duftite from Benahadux, Almeria, Andalusia, Spain. Specimen size 2.4 cm
General
Category	Arsenate minerals
Formula (repeating unit)	PbCuAsO4(OH)
Strunz classification	08.BH.35
Dana classification	41.5.1.4
Crystal system	Orthorhombic 222 disphenoidal
Unit cell	a = 7.768(1) Å, b = 9.211(1) Å, c = 5.999(1) Å; Z=4
Identification
Formula mass	426.67 g
Color	Green, olive green or grey green. Generally zoned due to compositional variations
Crystal habit	Tiny crystals elongated along [001] with curved and rough faces, aggregated into crusts. Crystals may be pseudo-octahedral.
Crystal symmetry	Orthorhombic 222
Cleavage	Indistinct
Fracture	Uneven to conchoidal
Mohs scale hardness	4.5
Luster	Vitreous on fracture surfaces and dull on crystal faces
Streak	Pale green or white
Diaphaneity	Crystals are transparent to translucent
Specific gravity	6.4 (measured), 6.60 (calculated)
Optical properties	Biaxial (-)
Refractive index	nα = 2.03–2.04, nβ = 2.06–2.08, nγ = 2.08–2.10
Birefringence	δ = 0.06
2V angle	Large
Dispersion	r > v, perceptible
Other characteristics	Decrepitates on heating. Not radioactive.
References	[1][2][3]

Duftite is a relatively common arsenate mineral with the formula CuPb(AsO₄)(OH), related to conichalcite. It is green and often forms botryoidal aggregates. It is a member of the adelite-descloizite Group, Conichalcite-Duftite Series. Duftite and conichalcite specimens from Tsumeb are commonly zoned in color and composition. Microprobe analyses and X-ray powder-diffraction studies indicate extensive substitution of Zn for Cu, and Ca for Pb in the duftite structure. This indicates a solid solution among conichalcite, CaCu(AsO₄ )(OH), austinite, CaZn(AsO₄)(OH) and duftite PbCu(AsO₄)(OH), all of them belonging to the adelite group of arsenates.^[4] It was named after Mining Councilor G Duft, Director of the Otavi Mine and Railroad Company, Tsumeb, Namibia.^[5] The type locality is the Tsumeb Mine, Tsumeb, Otjikoto Region, Namibia.

Structure

The structure^[6] is composed of chains of edge-sharing CuO₆ distorted octahedra parallel to the c axis. The chains are linked by AsO₄ tetrahedra and Pb atoms.

Environment

Duftite is an uncommon product of weathered sulfide ore deposits. It is associated with azurite at the type locality,^[5] and with bayldonite, segnitite, agardite and gartrellite at the Central Cobar Mines, New South Wales, Australia, where some pseudomorphs of duftite after mimetite have also found.^[7] It occurs in association with olivenite, mottramite, azurite, malachite, wulfenite and calcite in the Tsumeb, Namibia deposit. It occurs with bayldonite, beudantite, mimetite and cerussite in the Cap Garonne mine, France.^[3]

Duftite on cerussite, Tsumeb mine, Namibia. Size: 6×5×3 cm.

Distribution

Reported from Argentina, Australia, Austria, Chile, the Czech Republic, France, Germany, Greece, Italy, Japan, Mexico, Namibia, Poland, Portugal, Russia, South Africa, Spain, Switzerland, the UK, the US and Zimbabwe.^[2]

References

1. Duftite. Webmineral.com. Retrieved on 2011-10-10.
2. Duftite. Mindat.org
3. Duftite. (PDF) Handbook of Mineralogy
4. Jambor, J L, Owens, D R and Dutrizac, J E (1980). "Solid solution in the adelite group of arsenates" (PDF). Canadian Mineralogist 18: 191–195.
5. Wherry E T and Foshag W F (1921). "New mineral names" (PDF). American Mineralogist 6: 140–141.
6. Kharisun; Max R. Taylor; D. J. M. Bevan; Allan Pring (1998). "The crystal chemistry of duftite, PbCuAsO4(OH) and the beta-duftite problem" (PDF). Mineralogical Magazine 62: 121–130. doi:10.1180/002646198547413.
7. Australian Journal of Mineralogy 11 (2): 79. Missing or empty |title= (help)