Arsendescloizite

Arsendescloizite


Composition: PbZn(AsO4)(OH)
Crystal System : Orthorhombic
Colours: Pale-yellow, lemon-yellow, green, dark-green
Lustre : Sub-vitreous
Hardness (H) : 4
Specific Gravity (S.G) : 6.57
Year of Discovery: 1979
IMA Number: 1979-030
IMA Status: Approved
Discovered By: Wolfgang Bartelke (German collector)
Named for: Composition/relationship (to descloizite)

Tsumeb is the Type Locality

Distribution

Very rare.

Occurrence

  • Supergene
  • 2nd Oxidation Zone

Notable Finds

The published description of arendescloizite (Keller and Dunn, 1982a) does not record the level in the mine from which the type material was recovered. There is some evidence to suggest, however, that it may have originated from 30 Level in the second oxidation zone.

Paragenetic and General Notes

Arsendescloizite visually resembles adamite, or even tsumcorite. It's X-ray pattern is closely similar to that of descloizite, and it is named for its chemical and crystallographic relationship with that mineral. Arsendescloizite is the end-member of a continuous (?) series with descloizite; however, no V, Cu, or Ca was detected in the type material.

On the type specimen, arsendescloizite occurs on a matrix of copper sulphides comprising mainly tennantite and chalcocite.  It is associated with willemite, chalcocite (crystals), quartz, goethite, and corroded mimetite.  Keller and Dunn (op. cit.) propose the following paragenesis:  chalcocite >> quartz >> mimetite >> arsendescloizite >> goethite >> willemite.

A specimen in the collection of Museum Victoria, in Australia (# M31461) shows dark-green arsendescloizite in association with wulfenite and tsumcorite.  Microprobe analysis of this dark green arsendescloizite has shown that is is a calcian cuprian variety, "intermediate in the chemical series between arsendescloizite, duftite, and conichalcite" (Mills and Birch, 2007). 

Arsendescloizite is reported to form pseudomorphs after mimetite (rare; Mills and Birch, 2007).