Arseniosiderite Locality: Roman?che-Thorens, Sa?ne-et-Loire, Rh?ne-Alpes, France (TYPE LOCALITY for BOTH SPECIES) Size: small cabinet, 6.4 x 6.2 x 5.6 cm Arseniosiderite in Romancheite A very rich specimen with shiny tigers-eye-like veins of arseniosiderite running through matrix of rich, massive Romancheite. The arseniosiderite is technically crystallized, forming lamellar crystals completely filling the veins they grew in. Ex. Jean Chervet Collection. — Photo: Robert M. Lavinsky · CC BY-SA 3.0
Arseniosiderite
A rare arsenate produced when minerals such as scorodite or arsenopyrite oxidize.
Intro adapted from Wikipedia (CC BY-SA).
Arseniosiderite is an IMA-recognized mineral species in the arsenate class, with the chemical formula Ca₂Fe³⁺₃O₂(AsO₄)₃·3H₂O.
It crystallizes in the monoclinic crystal system (space group A2/a). It is a member of the Arseniosiderite structural group.
Key properties: Mohs hardness 4.5; specific gravity 3.58–3.6; Ocher-yellow streak; Submetallic to silky luster; optically biaxial.
IMA symbol Assd, grandfathered status — known before the IMA’s founding, named in 1842.
A rare secondary mineral formed by the oxidation of earlier arsenic-bearing minerals, typically scorodite or arsenopyrite.
It is found associated with Beudantite, carminite, scorodite, dussertite, pharmacolite, pitticite, adamite, erythrite, arsenopyrite, löllingite.
The name refers to essential arsenic in the composition, and sideros, Greek for iron.