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Formula: PbZn(VO4)(OH)
Anhydrous vanadate containing hydroxyl,
adelite-descloizite group
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
Environments
Descloizite is a secondary mineral often found in the
oxidation zones of metal ore deposits in association with mottramite in
ore bodies containing vanadinite,
pyromorphite, mimetite and
cerussite. It has been found as
pseudomorphs after
vanadinite
(Dana).
Localities
At the Nakhlak Mine, Anarak District, Nain County, Isfahan Province, Iran, epigenetic (formed later than the
surrounding or underlying rock formation) vein deposits and metasomatic replacement bodies are hosted by a chalky
Upper Cretaceous (100.5 to 66 million years ago) limestone. The
limestone underwent
dolomitisation prior to sulphide mineralisation. The principal
primary ore mineral is
galena, associated with minor or trace amounts of
sphalerite, tetrahedrite
-tennantite, pyrite and
chalcopyrite as inclusions. The main
secondary ore mineral is
cerussite, sometimes associated with minor amounts of
anglesite, plattnerite,
wulfenite, minium,
mimetite, covellite,
chalcanthite, malachite and
goethite. Many trace elements are present in the
primary galena, but
most notably it is rich in silver and
antimony and poor in bismuth.
Dark green, drusy descloizite occurs with some specimens of red
mimetite and orange wulfenite
(Minrec 54.3.383-408).
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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