Formula: PbZn(VO4)(OH) anhydrous vanadate containing hydroxyl
Specific gravity: 6.2
Hardness: 3 to 3½
Streak: Orange to brownish-red
Colour: Brownish red, red-orange, reddish brown to blackish brown, nearly black
Solubility: Readily soluble in acids
Common impurities: Cu
Descloizite is a secondary mineral often found in the oxidation zones
of metal ore deposits in association with mottramite in ore bodies containing
mimetite and cerussite. It has been found as
pseudomorphs after vanadinite
Berg Aukas Mine, Namibia, is the world's best locality for crystallised specimens of descloizite; descloizite pseudomorphs after vanadinite and descloizite-coated vanadinite crystals have been found here.
Seven modes of occurrence of descloizite have been reported:
1. In minor amounts with massive first-formed willemite
2. With massive smithsonite as large well formed crystals in cavities
3. With calcite as infillings in large cavities and fissures where the surfaces were lined with vuggy descloizite and calcite
4. As narrow cross-cutting veinlets of descloizite with dolomite, in massive willemite
5. in isolation, with no associated secondary minerals
6. Fine grained, mixed with limonitic clay and calcite, dolomite, goethite-hematite, quartz and willemite
7. As black crystals in open cavities with massive goethite and minor hematite and pyrite (R&M 96.2.124-130)
At the Whitwell quarry, Derbyshire, England, UK, descloizite occurs on dolomite, associated with vanadinite (RES p137, 138)
At the Mammoth Mine, Arizona, USA, descloizite occurs with mottramite (Dana).
At the Kabwe mine, Central Province, Zambia, descloizite is an abundant mineral associated with tarbuttite or with smithsonite. It also occurs as thin lamellae in vanadinite (R&M 94.2.125).
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