Vivianite - Encyclopedia

    Class : Phosphates, arsenates, vanadates
    Subclass : Hydrated phosphate
    Crystal system : Monoclinic
    Chemistry : Fe3(PO4)2 . 8H2O
    Rarity : Common

Vivianite is the most common of iron phosphates of secondary origin. It owes its name to the English mineralogist John Henry Vivian who discovered it in English Cornwall at the beginning of the XVIIIth century. Vivianite is formed in oxidation zones of sulphide deposits, in pegmatites as a mineral resulting from the alteration of iron phosphates, in coal mines or in phosphorus-rich sedimentary deposits. It often crystallizes in elongated prisms sometimes grouped in rosettes. It is also found in tabular crystals, fibrous masses or bright blue encrustations. It has a characteristic perfect cleavage that disintegrates it into flexible blades and a low hardness that allows to scratch with the nail. Dark green when it is recently extracted, its exposure to the air usually causes a blue color variation by oxidation of ferrous iron and a pseudomorphosis in other iron phosphates which opacify it completely. Its conservation in collection result in some problems. Because of its attractive green color, vivianite is a sought after mineral for collectors, however it is not used in any particular field and it is rarely cut for jewelry.

Vivianite sprays from Kerch Mine, Crimean Peninsula, Ukraine
Vivianite from Huanuni mine, Oruro, Bolivia
Vivianite mega-crystals from Anloua, Cameroon
Vivianite cabochon from Australia

Vivianite in the World

The most spectacular crystals of vivianite are up to 4.5 m long, but they are totally altered and pseudomorphed. They were discovered in the phosphorus sedimentary formations of Anloua in Cameroon. Translucent dark green crystals quickly oxidized and dehydrated, they were commonly grouped in rosettes exceeding one meter ! This is an example of gigantism in the mineral world. Except for this deposit, the crystals do not exceed 20 cm. In addition to Anloua, the most beautiful specimens are bright and transparent critters of a dark green from stanniferous veins in Bolivia. Magnificent crystals were also extracted from Trepca in Kosovo (10 cm dark green crystals on siderite), Bingham in Utah (12 cm), Blackbird mine in Idaho (5 cm), Santa Eulalia in Mexico (8 cm). cm) and several in English Cornwall (St Just, Kea, St Agnes, etc ...). We also mention pegmatites from Brazilian Minas Gerais (Lavra do Enio and Lavra da Ilha) for their superb crystals exceeding 10 cm.

Vivianite in France

In France, vivianite is known in centimetric crystals in the upper levels of the Salsigne gold mine (Aude) and centimetric gemmy crystals in the Commentry (Allier) coal mines.

Twinning and special crystallization

Vivianite crystals twinned on {010}, according to its main cleavage plane, which often makes it difficult to detect.

Due to its sometimes sedimentary geology, it is not uncommon to find some fossils partially transformed into vivianite, the best example is probably the bivalves of Kerch in Ukraine.

Fakes and scams

No fake known for this mineral species.

Hardness : 1.5 to 2
Density : 2.68
Fracture : Fibrous
Trace : White, blue, brown

TP : Transparent to opaque
IR : 1.579 to 1.675
Birefringence : 0.050 to 0.059
Optical character : Biaxial +
Pleochroism : Blue, green, yellow
Fluorescence : None

Solubility : Acids

Magnetism : None
Radioactivity : None