Pharmacosiderite

arsenate

limonite

Formula: KFe3+4(AsO4)3(OH)4.6-7H2O
Specific gravity: 2.797
Hardness: 2½
Streak: White
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.
Environments:

Hydrothermal environments

Pharmacosiderite is a secondary mineral occurring in the oxidised zones of iron-bearing sulphide deposits or in hydrothermal deposits. Pharmacosiderite alters to limonite and manganese oxides, and forms pseudomorphs after siderite.
Common impurities: P

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