A 6x4 cm specimen of paramorphosed olive-green to green Metavivianite after oxidized vivianite. From Kerchenskoe deposit, Crimea Oblast, Ukraine. Photo and collection specimen by Pavel Kartashov. — Photo: VivianN Z · CC BY-SA 4.0
Metavivianite
A hydrated iron phosphate formed when vivianite oxidizes — the dark alteration seen on vivianite crystals.
Intro adapted from Wikipedia (CC BY-SA).
Metavivianite is an IMA-recognized mineral species in the phosphate class, with the chemical formula Fe²⁺Fe³⁺₂(PO₄)₂(OH)₂·6H₂O.
It crystallizes in the triclinic crystal system (space group P-1). It is a member of the Symplesite structural group.
Key properties: specific gravity 2.69; optically biaxial.
IMA symbol Mviv, IMA status: approved, named in 1973.
A secondary mineral typically formed from oxidizing vivianite, in complex granite pegmatites; authigenic, in bogs and soils.
It is found associated with Kryzhanovskite, triphylite (Big Chief mine, South Dakota, USA); vivianite (many authigenic occurrences).
The prefix meta- denotes the dehydration product of vivianite.