Descloizite, (with wulfenite)

Descloizite


Composition: PbZn(VO4)(OH)
Crystal System : Orthorhombic
Colours: Brown, brownish-red, orange-red, brownish-black
Lustre : Sub-vitreous, resinous, waxy, greasy
Hardness (H) : 3.0-3.5
Specific Gravity (S.G) : 6.2
References: Strunz et al. (1958a)

Distribution

Very rare. In the upper portions of both the first and second oxidation zones.

Occurrence

  • Supergene
  • 1st Oxidation Zone
  • 2nd Oxidation Zone

Notable Finds

On 28 Level, in the late 1980s, (Rob Bowell, personal communication to M.Southwood, 2014)

Paragenetic and General Notes

Descloizite is a very rare mineral at Tsumeb. Lombaard et al. (1986) note that vanadium mineralisation (chiefly as mottramite) is concentrated at the top of the first oxidation zone (between surface and 4 Level), and that there is a similar concentration at the top of the second oxidation zone. Gebhard (1999) notes that vanadium mineralisation was restricted, essentially, to an interval between 50 m and 100 m below surface, and that descloizite was found, rarely, in that zone.  In the second oxidation zone, Rob Bowell (2014, personal communication to M. Southwood) records having collected descloizite with vanadinite on 28 Level in the late 1980s.

Notwithstanding the rarity of descloizite at Tsumeb, there are several important (and prolific) descloizite localities nearby in the Otavi Mountainland.  Not surprisingly, descloizite specimens from these other localities have commonly been exported as part of consignments of "Tsumeb minerals" leading to incorrect locality attributions. 

Descloizite is sufficiently rare at Tsumeb that specimens attributed to the mine should be regarded with caution unless there is clear supporting evidence in the form of associated minerals, matrix composition, etc.

Descloizite is reported to form pseudomorphs after the following minerals:  calcite (rare, doubtful validity); pyromorphite (rare, doubtful validity).