Vivianite

phosphate

gossan

Formula: Fe2+3(PO4)2.8H2O
Hydrated phosphate, vivianite group
Specific gravity: 2.6 to 2.7
Hardness: 2
Streak: White to faintly light blue
Colour: Green to blue
Solubility: Readily soluble in hydrochloric acid and sulphuric acid; Slightly soluble in nitric acid
Environments:

Pegmatites
Sedimentary environments
Hydrothermal environments

Vivianite is a rare secondary mineral which is a weathering product of primary iron and manganese phosphates in granite pegmatites, in the oxidation zone of metal ore deposits, particularly associated with gossan, in the oxidation zone of hypothermal (high temperature) hydrothermal veins, in clay sediments, and in recent alluvial deposits replacing organic material, peat, lignite, bog iron ores and forest soils.

Common impurities: Mn,Mg,Ca

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