vivianite

{{Infobox mineral |boxbgcolor=#3f9d5b| name = Vivianite | category = Phosphate mineral Vivianite group | image = 7314M-vivianite2.jpg | caption = Vivianite tabular crystal, transparent, with a deep green color. Crystal size: 82 mm × 38 mm × 11 mm. From Huanuni mine, Dalence Province, Oruro Department, Bolivia | formula = | IMAsymbol = Viv | molweight = 501.61 g/mol | strunz = 8.CE.40 (10 ed)7/C.13-40 (8 ed) | dana = 40.3.6.1 | system = Monoclinic | class = Prismatic (2/m) (same H-M symbol) | symmetry = C2/m | unit cell = a = 10.086 Å, b = 13.441 Å c = 4.703 Å; β = 104.27°; Z = 2 | color = Colorless, very pale green, becoming dark blue, dark greenish blue, indigo-blue, then black with oxidation | habit = Flattened, elongated prismatic crystals, may be rounded or corroded; as stellate groups, incrustations, concretionary, earthy or powdery | twinning = Translation gliding | cleavage = Perfect on {010} | fracture = Fibrous | tenacity = Flexible, sectile | mohs = 1.5–2 | luster = Vitreous, pearly on the cleavage, dull when earthy | streak = White, altering to dark blue, brown | diaphaneity = Transparent to translucent | gravity = 2.68 | density = | polish = | opticalprop = Biaxial (+); moderate relief | refractive = nα = 1.579–1.616, nβ = 1.602–1.656, nγ = 1.629–1.675 | birefringence = δ = 0.050–0.059 | pleochroism = Visible; X = blue, deep blue, Indigo-blue; Y = pale yellowish green, pale bluish green, yellow-green; Z = pale yellowish green, olive-yellow | 2V = Measured: 63° to 83.5°, Calculated: 78° to 88° | dispersion = r 2+, magnesium Mg2+, and calcium Ca2+ may substitute for iron Fe2+ in its structure. Pure vivianite is colorless, but the mineral oxidizes very easily, changing the color, and it is usually found as deep blue to deep bluish green prismatic to flattened crystals. Vivianite crystals are often found inside fossil shells, such as those of bivalves and gastropods, or attached to fossil bone. Vivianite can also appear on the iron coffins or on the corpses of humans as a result of a chemical reaction of the decomposing body with the iron enclosure.

It was named by Abraham Gottlob Werner, the "father of German geology", in 1817, the year of his death, after either John Henry Vivian (1785–1855), a Welsh-Cornish politician, mine owner and mineralogist living in Truro, Cornwall, England, or after Jeffrey G. Vivian, an English mineralogist. Vivianite was discovered at Wheal Kind, in St Agnes, Cornwall.