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Formula: ZnPb10(CrO4)6(SiO4)2(OH)2
Compound chromate
Crystal System: Triclinic
Specific gravity: 6.42 measured, 6.50 calculated
Hardness: 3
Streak: Saffron yellow
Colour: Bright orange to henna-brown to nearly black
Environments:
Hemihedrite is formed through oxidation of galena,
sphalerite and pyrite in the
oxide zone of hydrothermal lead-bearing veins.
At the Rat Tail claim, Maricopa county, Arizona, USA, hemihedrite is formed by the oxidation of
galena, sphalerite and
pyrite in quartz veins cutting
andesite. The assemblage consists largely of hemihedrite,
willemite, cerussite and
phoenicochroite, with minor amounts of
mimetite and vauquelinite
(AM 55.1088-1102).
At the type locality, the Florence Mine, Pinal county, Arizona, USA, hemihedrite occurs in the oxidised zone of
lead-bearing veins that cut limestone intruded by an
altered porphyry (rock with coarse phenocrysts in a finer groundmass) and
quartzite
(Mindat),
associated with cerussite, phoenicochroite,
vauquelinite, willemite,
galena, sphalerite,
pyrite, tennantite and
chalcopyrite
(HOM, AM 53.1421-1427).
The sequence of formation is cerussite first, followed by hemihedrite and
wulfenite, with wulfenite continuing to
crystallise after hemihedrite, and vauquelinite last
(AM.55.1088-1102).
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