PHARMACOSIDERITE, a mineral species consisting of hydrated basic ferric arsenate, 2FeAs04 Fe(OH)3.5H20.
A curious property is to be observed when a crystal of pharmacosiderite is placed in a solution of ammonia - in a few minutes the green colour changes throughout the whole crystal to red; on placing the red crystal in dilute hydrochloric acid the green colour is restored.
Pharmacosiderite is a mineral of secondary origin, the crystals occurring attached to gozzany quartz in the upper part of veins of copper ore.
Normal ferric arsenate, FeAs0 4.2H2O, constitutes the mineral scorodite; pharmacosiderite is the basic arsenate 2FeAsO4Fe(OK)3.5H2O.
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