Duftite

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.[5] It was named after Mining Councilor G Duft, Director of the Otavi Mine and Railroad Company, Tsumeb, Namibia.[1] The type locality is the Tsumeb Mine, Tsumeb, Otjikoto Region, Namibia.

Duftite
Anglesite-Duftite-174037.jpg
Duftite from Tsumeb Mine, Tsumeb, Otjikoto Region, Namibia
General
CategoryArsenate minerals
Formula
(repeating unit)
PbCuAsO4(OH)
Strunz classification8.BH.35
Dana classification41.5.1.4
Crystal systemOrthorhombic
Crystal classDisphenoidal (222)
H-M symbol: (2 2 2)
Space groupP212121
Unit cella = 7.768(1), b = 9.211(1)
c = 5.999(1) [Å]; Z = 4
Identification
Formula mass426.67 g/mol
ColorGreen, olive green or grey green. Generally zoned due to compositional variations.
Crystal habitTiny crystals elongated along [001] with curved and rough faces, aggregated into crusts. Crystals may be pseudo-octahedral.
CleavageIndistinct
FractureUneven to conchoidal
Mohs scale hardness4.5
LusterVitreous on fracture surfaces and dull on crystal faces
StreakPale green or white
DiaphaneityCrystals are transparent to translucent
Specific gravity6.4 (measured), 6.60 (calculated)
Optical propertiesBiaxial (-), faint apple-green color (transmitted light)
Refractive indexnα = 2.03–2.04, nβ = 2.06–2.08, nγ = 2.08–2.10
Birefringenceδ = 0.06
2V angleLarge
Dispersionr > v, perceptible
SolubilityReadily soluble in acids[1]
Other characteristicsDecrepitates on heating. Not radioactive.
References[2][3][4]

StructureEdit

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.

EnvironmentEdit

Duftite is an uncommon product of weathered sulfide ore deposits. It is associated with azurite at the type locality,[1] 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.[4]

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

DistributionEdit

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.[3]

ReferencesEdit

  1. ^ a b c Wherry ET, Foshag WF (1921). "New mineral names" (PDF). American Mineralogist. 6: 140–141.
  2. ^ Duftite. Webmineral.com. Retrieved on 2011-10-10.
  3. ^ a b Duftite. Mindat.org
  4. ^ a b Duftite. (PDF) Handbook of Mineralogy
  5. ^ 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.CS1 maint: multiple names: authors list (link)
  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 (1): 121–130. Bibcode:1998MinM...62..121K. doi:10.1180/002646198547413.
  7. ^ Australian Journal of Mineralogy. 11 (2): 79. Missing or empty |title= (help)

BibliographyEdit

  • Palache, P.; Berman H.; Frondel, C. (1960). "Dana's System of Mineralogy, Volume II: Halides, Nitrates, Borates, Carbonates, Sulfates, Phosphates, Arsenates, Tungstates, Molybdates, Etc. (Seventh Edition)" John Wiley and Sons, Inc., New York, pp. 810-811.