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Descloizite specimen from Berg Aukas (Berg Aukus), Namibia, 9.5 x 8.9 x 4.9 cm
Category Vanadate mineral
(repeating unit)
Strunz classification 08.BH.40
Crystal symmetry Orthorhombic (2/m 2/m 2/m) - dipyramidal
Unit cell a = 7.593 Å, b = 6.057 Å, c = 9.416 Å; Z = 4
Color Brownish red, red-orange, reddish to blackish brown, nearly black
Crystal habit Zoned tabular crystals common, encrustations and plumose aggregates
Crystal system Orthorhombic
Cleavage None
Fracture Irregular, sub-conchoidal
Tenacity Brittle
Mohs scale hardness 3 - 3.5
Luster Greasy
Streak Orange to brownish red
Diaphaneity Transparent to opaque
Specific gravity 6.1 - 6.2
Optical properties Biaxial (-)
Refractive index nα = 2.185 nβ = 2.265 nγ = 2.350
Birefringence δ = 0.165
Pleochroism Visible
2V angle 85° to 90°
Dispersion Strong r > v rarely r < v
References [1][2][3]

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.[4] 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.[4] There is also an arsenate analogue called arsendescloizite.[5]

Discovery and occurrence[edit]

Superb spear-point bladed crystals of Descloizite, Berg Aukas, Namibia. Size 3.6 x 3.1 x .9 cm.

It was discovered in the Sierra de Córdoba deposit in Córdoba, Argentina in 1854 and named in honor of the French mineralogist Alfred Des Cloizeaux (1817–1897).[1] It occurs as small prismatic or pyramidal crystals, usually forming drusy crusts and stalactitic aggregates; also as fibrous encrusting masses with a mammillary surface.[4]

Descloizite occurs in oxidised portions of veins of lead ores in association with pyromorphite, vanadinite, wulfenite, mottramite, mimetite and cerussite.[3]

The Otavi ("O-tarvi") Mountainland of northern Namibia was once considered home to the greatest vanadium deposits in the world, including those at Berg Aukas ("OW-cuss"), Abenab ("UB-en-ub"), Baltika ("BUL-tika") and Uitsab ("ATE-sub").[6] Descloizite and mottramite were the main ore minerals in each of these deposits, which are now exhausted. Other localities are the Sierra de Cordoba in Argentina; Lake Valley in Sierra County, New Mexico; Arizona; Phoenixville in Pennsylvania and Obir, Carinthia Austria.


  1. ^ a b
  2. ^ Webmineral data
  3. ^ a b Handbook of Mineralogy
  4. ^ a b c  One or more of the preceding sentences incorporates text from a publication now in the public domainChisholm, Hugh, ed. (1911). "Descloizite". Encyclopædia Britannica 8 (11th ed.). Cambridge University Press. p. 91. 
  5. ^ Arsendescloizite on
  6. ^ Boni et al., 2007, Genesis of vanadium ores in the Otavi Mountainland, Namibia. Economic Geology v.102 p.441-469.