Descloizite

Descloizite
Descloizite specimen from Berg Aukas (Berg Aukus), Namibia, 9.5 x 8.9 x 4.9 cm
General
CategoryVanadate mineral
Formula
(repeating unit)
(Pb,Zn)2VO4OH
IMA symbolDcz[1]
Strunz classification8.BH.40
Crystal systemOrthorhombic
Crystal classDipyramidal (mmm)
H-M symbol: (2/m 2/m 2/m)
Space groupPnma (no. 62)
Unit cella = 7.593, b = 6.057
c = 9.416 [Å]; Z = 4
Identification
ColorBrownish red, red-orange, reddish to blackish brown, nearly black
Crystal habitZoned tabular crystals common, encrustations and plumose aggregates
CleavageNone
FractureIrregular, sub-conchoidal
TenacityBrittle
Mohs scale hardness3 – 3.5
LusterGreasy
StreakOrange to brownish red
DiaphaneityTransparent to opaque
Specific gravity6.1 – 6.2
Optical propertiesBiaxial (−)
Refractive indexnα = 2.185 nβ = 2.265 nγ = 2.350
Birefringenceδ = 0.165
PleochroismVisible
2V angle85° to 90°
DispersionStrong r > v rarely r < v
References[2][3][4]

Descloizite is a rare mineral species consisting of basic lead and zinc vanadate, (Pb, Zn)2(OH)VO4, crystallizing in the orthorhombic crystal system and isomorphous with olivenite.[5] Appreciable gallium and germanium may also be incorporated into the crystal structure.

The color is deep cherry-red to brown or black, and the crystals are transparent or translucent with a greasy lustre; the streak is orange-yellow to brown; specific gravity 5.9 to 6.2; hardness 31/2. A variety known as cuprodescloizite is dull green in color; it contains a considerable amount of copper replacing zinc and some arsenic replacing vanadium.[5] There is also an arsenate analogue called arsendescloizite.[6]

  1. ^ Warr, L.N. (2021). "IMA–CNMNC approved mineral symbols". Mineralogical Magazine. 85 (3): 291–320. Bibcode:2021MinM...85..291W. doi:10.1180/mgm.2021.43. S2CID 235729616.
  2. ^ Descloizite on Mindat.org
  3. ^ Webmineral data
  4. ^ "Handbook of Mineralogy" (PDF). Archived from the original (PDF) on 2021-02-27. Retrieved 2010-11-15.
  5. ^ a b  One or more of the preceding sentences incorporates text from a publication now in the public domainChisholm, Hugh, ed. (1911). "Descloizite". Encyclopædia Britannica. Vol. 8 (11th ed.). Cambridge University Press. p. 91.
  6. ^ Arsendescloizite on Mindat.org