Formula: Ca2Fe3+3O2(AsO4)3.3H2O
Hydrated arsenate containing hydroxyl
Forms pseudomorphs after siderite and scorodite
Specific gravity: 3.60
Hardness: 4½, 1½ in fibres
Streak: ochre-yellow
Colour: Golden-yellow to yellow-brown, reddish-brown, brown, black; reddish brown to brownish yellow in transmitted light
Solubility: Readily soluble in hot acids

Hydrothermal environments

Arseniosiderite is a rare secondary mineral formed by the low-temperature oxidation of earlier arsenic-bearing minerals, such as scorodite, arsenopyrite and löllingite (Webmin). Associated Minerals at the type locality include quartz, psilomelane, hematite and goethite (Mindat).

At Hūttenberg, Carinthia, Austria, arseniosiderite occurs in felted masses with scorodite, symplesite, pitticite and pharmacolite on löllingite.

At Romanêche-Thorins, Saône et Loire, France, arseniosiderite occurs in a manganese deposit with quartz, goethite, romanèchite and psilomelane (Dana).

At Schneeberg, Bavaria, Germany, arseniosiderite occurs with erythrite and roselite Dana.

At the Jesus Maria Mine, Mazapil district, Mexico, arseniosiderite occurs with pharmacolite, chrysocolla and calcite, and as pseudomorphs after scorodite. (Dana)

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