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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 the Majuba Hill Mine, Antelope Mining District, Pershing County, Nevada, USA, pharmacosiderite has been found
with arthurite
(Mindat photo).
Pharmacosiderite from Majuba Hill -
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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