Formula: Fe2+3(PO4)2 · 8H2O

Colour: Colourless and transparent when fresh, quickly turning pale to deep blue, greenish-blue or bluish-green.

Lustre: Vitreous, Pearly, Dull

Hardness: 1½ – 2

Specific Gravity: 2.67 – 2.69

Crystal System: Monoclinic

Member of: Vivianite Group

Name: Named by Abraham Gottlob Werner in 1817 after John Henry Vivian (1785-1855), an English (Welsh-Cornish) politician, mine owner, and mineralogist living in Truro, Cornwall and discoverer of the mineral.

Type Locality: Wheal Kine (Wheal Kind), St Agnes Consols (Polberro Consols), St Agnes, Cornwall – England, UK

Dimorph of: Symplesite Group

Usually found as deep blue to deep bluish green prismatic to flattened crystals, most crystals rather small to microscopic, larger ones rather rare. When fresh the mineral may be colourless, or nearly so, and, once exposed, will oxidize with the Fe2+ converting to Fe3+ with a concurrent darkening to dark blue or blue-green. Exposure to light will ultimately allow this darkening to continue until the specimen is almost black and opaque. This exposure is irreversible and inevitable with any vivianite sample left in the light.