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 symmetry Orthorhombic 222
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 system Orthorhombic 222 disphenoidal
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 colour 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 USA and Zimbabwe.[2]

References

  1. ↑ Duftite. Webmineral.com. Retrieved on 2011-10-10.
  2. ↑ 2.0 2.1 Duftite. Mindat.org
  3. ↑ 3.0 3.1 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. ↑ 5.0 5.1 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, and 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)
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