Formula: KFe3+4(AsO4)3(OH)4.6-7H2O
Hydrated arsenate containing hydroxyl
Specific gravity: 2.797
Hardness: 2½
Streak: Yellowish green
Colour: Green, brown, yellow, red. Light brown in transmitted light.
Solubility: Soluble in hydrochloric acid. Green crystals immersed in ammonia turn red and revert to the original green colour when reimmersed in dilute hydrochloric acid.
Common impurities: P

Hydrothermal environments

Pharmacosiderite is a secondary mineral typically found, along with scorodite, as an oxidation product of arsenopyrite in the oxidised zones of iron-bearing sulphide deposits or in hydrothermal deposits. It may also develop during oxidation of other iron-bearing sulphides such as pyrite or chalcopyrite in the presence of arsenate ions produced by the decomposition of other primary arsenic-bearing phases (Mindat, MW). Associated minerals include scorodite, beudantite, carminite, erythrite, arseniosiderite, symplesite, jarosite, pitticite and limonite (HOM, Mindat).


At Bou Azzer Mine, Amerzgane, Ouarzazate Province, Drâa-Tafilalet Region, Morocco pharmacosiderite is a product of the weathering of iron-rich ores, especially löllingite. It forms crusts of crystals ~0.1 mm with erythrite in a quartz matrix (Minrec 38.5.387).

At Méchoui 1, Amerzgane, Ouarzazate Province, Drâa-Tafilalet Region, Morocco, pharmacosiderite crystals to 2 mm occur with erythrite on a matrix of weathered löllingite (Minrec 38.5.387).

At Oumlil East Mine, Oumlil, Zagora Province, Drâa-Tafilalet Region, Morocco, surfaces encrusted with pharmacosiderite crystals to 1 mm often serve as substrates for crystals of other minerals, including karibibite (Minrec 38.5.387).

At Tamdrost, Zagora Province, Drâa-Tafilalet Region, Morocco, pharmacosiderite crystals ~0.2 mm occur with olivenite and lavendulan (Minrec 38.5.387).

There are two co-type localities, the Tincroft Mine, Pool, Carn Brea, and the Carharrack Mine, Carharrack, Gwennap, both in Cornwall, England, UK

At Burdell Gill, Coombe Height, Caldbeck, Allerdale, Cumbria, England, UK, pharmacosiderite is the most abundant of the supergene arsenate minerals. It occurs as crystals to 2mm lining cavities in the gossanous quartz - goethite - cryptomelane vein material or on botryoidal goethite (JRS 8(1).5-6).

At Gwaith-yr-Afon Mine, Goginan, Ceredigion, Wales, UK, pharmacosiderite occurs as small (0.25 mm) cubic crystals in thin drusy crusts on goethite and quartz in proximity to heavily corroded chalcopyrite. Probable scorodite is the only other associated supergene mineral (MW).

At the San Rafael mine, Quartz Mountain camp, Lodi Mining District, Lodi Hills, Nye county, Nevada, USA pharmacosiderite has been found as crystals to 0.1 mm associated with jarosite 9R&M 85.6.520).

At mines in the Tintic district, Utah, USA, pharmacosiderite occurs with scorodite and copper arsenates derived from enargite (Dana).

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