Formula: Fe2+3(AsO4)2.8H2O
Hydrated normal arsenate, vivianite group (Dana), may be intergrown with its dimorph, parasymplesite (Mindat).
Specific gravity: 2.96 to 3.01
Hardness: 2½
Streak: White, bluish white
Colour: Light green, greenish black, light blue, indigo blue
Solubility: Soluble in acids. Turns reddish brown in strong KOH solution or in 30% H2O2. Mindat

Hydrothermal environments

Symplesite is a rare secondary mineral in the oxidised zone of some arsenic-rich hydrothermal mineral deposits, associated with pharmacosiderite, scorodite, erythrite, roselite, annabergite, parasymplesite and limonite (HOM, Mindat).

At the type locality, Tännig, Bad Lobenstein, Thuringia, Germany, symplesite occurs in the oxidised zone of arsenic-bearing hydrothermal deposits, associated with scorodite, roselite, pharmacosiderite, parasymplesite, erythrite and annabergite (Mindat).

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