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Formula: KFe3+4(AsO4)3(OH)4.6-7H2O
Hydrated arsenate containing hydroxyl
Crystal System: Isometric
Specific gravity: 2.797 measured, 2.90 calculated
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
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).
Localities
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).
Pharmacosiderite from Bou Azzer - Image
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).
Pharmacosiderite from Méchoui - Image
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).
Pharmacosiderite from Oumlil - Image
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.
Pharmacosiderite from Carharrack - Image
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).
Pharmacosiderite from Burdell Gill - Image
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).
Pharmacosiderite from San Rafael - Image
At mines in the Tintic district, Utah, USA, pharmacosiderite occurs with
scorodite and copper
arsenates derived from enargite
(Dana).
Pharmacosiderite has been found at the Mammoth, Gold Chain, Trixie and Colorado #1 mines
(MinRec 55.2.217-218).
Pharmacosiderite from Tintic - Image
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