Formula: Ca4Mg(AsO3OH)2(AsO4)2.11H2O
Hydrated acid arsenate
Specific gravity: 2.58
Hardness: 1 to 2
Streak: White
Colour: White, colorless in transmitted light

Hydrothermal 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 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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