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Red phoenicochroite and orange hemihedrite microcrystals richly cover the matrix
Category Chromate mineral
(repeating unit)
Strunz classification 7.FC.15
Crystal system Triclinic
Unknown space group
Unit cell a = 9.49, b = 11.44
c = 10.84 [Å]; α = 120.5°
β = 92.1°, γ = 55.83°; Z = 1
Color Bright orange, henna-brown, to almost black
Crystal habit Euhedral crystals with hemihedral morphology
Twinning Present
Mohs scale hardness 3
Luster Vitreous
Streak Saffron-yellow
Diaphaneity Translucent to transparent
Specific gravity 6.42
Optical properties Biaxial (+)
Refractive index nα = 2.105 nβ = 2.320 nγ = 2.650
Birefringence δ = 0.545
Pleochroism Feeble, yellow to orange
2V angle 88° (measured)
References [1][2][3][4]

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]

Discovery and occurrence[edit]

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]