Formula: Ca(AsO3OH).2H2O
Hydrated acid arsenate
Specific gravity: 2.53 to 2.73
Hardness: 2 to 2½
Streak: White
Colour: White or colourless, greyish white; colourless in transmitted light
Solubility: Readily soluble in acids; insoluble in water.

Hydrothermal environments

Pharmacolite is an uncommon secondary mineral formed by oxidation of earlier arsenic-bearing minerals and commonly associated with haidingerite, picropharmacolite and hornesite (HOM, Mindat). It dehydrates rapidly at 60°C to haidingerite (Mindat).

At the type locality, the Sophia Mine, Baden-Württemberg, Germany, pharmacolite is found on oxidised arsenic ores, and may be post-mining. It is associated with calcium-rich rösslerite and haidingerite (Mindat).

At Bou Azzer, Morocco, pharmacolite forms easily as a post-mining product and also in oxidation zones. In vein 7 it occurs as aggregates on quartz associated with picropharmacolite, erythrite and, more rarely, lavendulan. In vein 2 it occurs in arsenic-bearing cobalt ores associated with hematite, spherocobaltite and picropharmacolite. It has been found on a diorite matrix with gypsum and lavendulan. At Méchoui and Ightem it is intergrown with picropharmacolite and associated with heterogenite (Minrec 38.5.387).

At the OK mine, Los Angeles county, USA, pharmacolite occurs with erythrite (Dana).

At White Caps mine, Nevada, USA, pharmacolite is found with other arsenates, especially haidingerite (Dana).

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