Erythrite Locality : Bou Azzer, Bou Azzer District, Tazenakht, Ouarzazate Province, Souss-Massa-Draâ Region, Morocco Size : 5.5 x 4.5 x 3 cm; XX1.7cm — Photo: Didier Descouens · CC BY-SA 3.0
Erythrite
Also known as: Cobalt bloom.
Hydrated cobalt arsenate — the crimson 'cobalt bloom' that coats cobalt ores and guides prospectors to them.
Intro adapted from Wikipedia (CC BY-SA).
Erythrite is an IMA-recognized mineral species in the arsenate class, with the chemical formula Co₃(AsO₄)₂·8H₂O.
It crystallizes in the monoclinic crystal system (space group C2/m). It is a member of the Vivianite structural group.
Key properties: Mohs hardness 1.5–2.5; specific gravity 3.06; typically red or pink or purple or gray; Pale red to pink streak; Subadamantine, pearly on cleavages luster; refractive index 1.664; optically biaxial.
IMA symbol Ery, grandfathered status — known before the IMA’s founding, named in 1832.
Found as a secondary mineral in the oxide zone of some Co–Ni–As-bearing mineral deposits.
It is found associated with Cobaltite, skutterudite, symplesite, roselite-beta, scorodite, pharmacosiderite, adamite, morenosite, retgersite, malachite.
Its name comes from the Greek for red, for its characteristic deep crimson color.
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