What is Vivianite?
Vivianite is a very soft hydrated iron phosphate famous for transparent crystals that can darken from pale green or colourless to blue and indigo on oxidation.
Mineralogy and structure
Reference formula: Fe3(PO4)2·8H2O. Vivianite is monoclinic and strongly hydrated. Fresh crystals can be light, while oxidation changes Fe2+ toward Fe3+ and deepens the colour. COD 1001782 is an exact structural reference. Vivianite is classified with phosphates and has monoclinic crystal symmetry. Typical hardness is 1.5–2 on the Mohs scale and specific gravity is approximately 2.6–2.7.
Colour, lustre and habit
Typical colours include colourless, pale green, blue, blue-green, deep indigo. The usual prismatic, bladed, radiating habit and vitreous, pearly, silky lustre help describe a specimen, but colour alone is not diagnostic.
Formation and notable localities
Vivianite forms in or is associated with phosphate-rich pegmatites, iron deposits, bog iron, organic sediments and secondary cavities. Important documented localities include Bolivia, Brazil, Cameroon, Romania, Russia, Ukraine, the United States and Australia.
A crystal that changes colour with time
Vivianite is one of the most compelling collector minerals because its blue colour is part of a chemical time story. Transparent blades, natural oxidation, matrix and provenance drive value.
Collecting and care
Extremely soft and fragile: keep dry, dark or softly lit as appropriate, avoid abrasion and heat, and support thin blades during display.
