Pharmacosiderite Dimensions: 32 mm x 15 mm x 12 mm Locality: Burdell Gill, Coombe Height, Caldbeck, Allerdale, Cumbria, England, UK Description: Honey brown vit — Photo: Anthea Strickland · Public domain
Pharmacosiderite
A hydrated potassium-iron arsenate forming tiny yellow-green cubes in oxidized arsenic deposits.
Intro adapted from Wikipedia (CC BY-SA).
Pharmacosiderite is an IMA-recognized mineral species in the arsenate class, with the chemical formula KFe³⁺₄(AsO₄)₃(OH)₄·6-7H₂O.
It crystallizes in the cubic crystal system (space group P-43m). It is a member of the Pharmacosiderite structural group.
Key properties: Mohs hardness 2.5; specific gravity 2.797; typically yellow or brown or red or green; white streak; Adamantine to greasy luster.
IMA symbol Pmsd, grandfathered status — known before the IMA’s founding, named in 1813.
An oxidation product of arsenic-bearing sulfides.
It is found associated with Scorodite, beudantite, carminite, arseniosiderite, symplesite, jarosite, “limonite”.
Its name comes from the Greek for poison, for the arsenic content, and iron in the composition.
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