Hemihedrite

Hemihedrite is a rare lead zinc chromate silicate mineral with formula Pb10Zn(CrO4)6(SiO4)2(F,OH)2. It forms a series with the copper analogue iranite.[2]

Hemihedrite
Red phoenicochroite and orange hemihedrite microcrystals richly cover the matrix
General
CategoryChromate mineral
Formula
(repeating unit)		Pb10Zn(CrO4)6(SiO4)2(F,OH)2
Strunz classification7.FC.15
Crystal systemTriclinic
Unknown space group
Unit cella = 9.49, b = 11.44
c = 10.84 [Å]; α = 120.5°
β = 92.1°, γ = 55.83°; Z = 1
Identification
ColorBright orange, henna-brown, to almost black
Crystal habitEuhedral crystals with hemihedral morphology
TwinningPresent
Mohs scale hardness3
LusterVitreous
StreakSaffron-yellow
DiaphaneityTranslucent to transparent
Specific gravity6.42
Optical propertiesBiaxial (+)
Refractive indexnα = 2.105 nβ = 2.320 nγ = 2.650
Birefringenceδ = 0.545
PleochroismFeeble, yellow to orange
2V angle88° (measured)
References[1][2][3][4]

Discovery and occurrence

Hemihedrite was first described in 1967 for occurrences in the Florence lead silver mine in the Ripsey District, Tortilla Mountains, Pinal County, Arizona, US.[2] It was named for the hemihedral morphology of its crystals.[1]

It occurs in oxidized veins containing galena, sphalerite and pyrite. Associated secondary minerals include cerussite, phoenicochroite, vauquelinite, willemite, wulfenite, galena, sphalerite, pyrite, tennantite and chalcopyrite.[1] It has been reported from several mining districts in Arizona and one in Nevada. It has also been reported from the Antofagasta Region of Chile and the Anarak District of Esfahan Province, Iran.[2]


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References
  1. Handbook of Mineralogy
  2. Hemihedrite on Mindat.org
  3. Hemihedrite data on Webmineral
  4. Mineralienatlas


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