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Formula: Ca4Mg(AsO3OH)2(AsO4)2.11H2O
Hydrated acid arsenate
Crystal System: Triclinic
Specific gravity: 2.55 to 2.642 measured, 2.58 calculated
Hardness: 1 to 2
Streak: White
Colour: White, colourless in transmitted light
Luminescence: Not fluorescent under UV
Environments:
Picropharmacolite is a secondary mineral formed in
the oxidation zone of arsenic ore deposits
(Webmin, Dana).
It is an oxidation product of arsenic-bearing sulphides in reaction
with surrounding
calcium-rich rocks, or as a recent efflorescence in mine workings. Associated minerals include
erythrite and
pharmacolite
(HOM).
The natural arsenates, including picropharmacolite, form at very
low pressure and temperature in the
oxidation zone of mineral deposits that contain arsenic
(AM59.807).
At the Shimen mine, Hunan, China, picropharmacolite lines vugs in massive
realgar
(Minrec 38.1.52).
At the Giftgrube mine, Sankt Jakob vein, Neuenberg, Sainte-Marie-aux-Mines, Colmar-Ribeauvillé, Haut-Rhin, Grand Est,
France, supergene picropharmacolite is one of the associates of smamite
(AM 105.4.555–560).
At the type locality, the ore dumps of the Richelsdorf Smelter, Hesse, Germany, picropharmacolite is
found as surface weathering of arsenic-bearing ores
(Mindat).
At Bou Azzer, Morocco, picropharmacolite is very common, sometimes associated with
sainfeldite. At the
Aghbar mine it is associated with erythrite,
sainfeldite and
pharmacolite, and at the Méchoui deposit it is associated
with erythrite and
spherocobaltite
(Minrec 38.5.387).
At Joplin, Missouri, USA, picropharmacolite has been found as a coating on
dolomite
(Dana).
At the White Caps mine, Nye county, Nevada, USA, picropharmacolite is associated with
realgar, gypsum
and sulphur
(Minrec 41.6.547).
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