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.^[3]

Hemihedrite
Red phoenicochroite and orange hemihedrite microcrystals richly cover the matrix
General
Category	Chromate mineral
Formula	Pb10Zn(CrO4)6(SiO4)2(F,OH)2
IMA symbol	Hhe[1]
Strunz classification	7.FC.15
Crystal system	Triclinic
Space group	P1 (No. 2)
Unit cell	a = 9.49, b = 11.44 c = 10.84 [Å]; α = 120.5° β = 92.1°, γ = 55.83°; Z = 1
Identification
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	[2][3][4][5][6]

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.^[3] It was named for the hemihedral morphology of its crystals.^[2]

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.^[2] 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.^[3]