Locality: Rat Tail claim (Pack Rat claim), Wickenburg area, Belmont Mts, Maricopa Co., Arizona, USA Dimensions: 3.3 cm x 2.9 cm x 1.2 cm Hemihedrite is a very rare Pb-Zn chromate and phoenicochroite is a very rare Pb-chromate. Red phoenicochroite and orange hemihedrite microcrystals richly cover the matrix on this excellent combination example from this obscure Arizona locale. Ex. Will Henderson Collection. Tim Blackwood Collection. — Photo: Robert M. Lavinsky · CC BY-SA 3.0
Hemihedrite
A rare lead-zinc chromate-silicate forming a series with the copper analogue iranite.
Intro adapted from Wikipedia (CC BY-SA).
Hemihedrite is an IMA-recognized mineral species in the silicate class, with the chemical formula ZnPb₁₀(CrO₄)₆(SiO₄)₂(OH)₂.
It crystallizes in the triclinic crystal system (space group P-1). It is a member of the Iranite structural group.
Key properties: Mohs hardness 3; specific gravity 6.42; Saffron-yellow streak; Vitreous luster; refractive index 2.358; optically biaxial.
IMA symbol Hhe, IMA status: approved, named in 1967.
Formed through oxidation of galena, sphalerite, and pyrite, in the oxide zone of hydrothermal lead-bearing veins.
It is found associated with Cerussite, phoenicochroite, vauquelinite, willemite, wulfenite, galena, sphalerite, pyrite, tennantite, chalcopyrite (Florence Lead-Silver mine, Arizona, USA).
In allusion to its distinctive hemihedral morphology.