Vivianite

File:Vivianite 2 w-triphylite and feldspar (Hydrous iron phosphate Custer County South Dakota 1652.jpg

Vivianite from South Dakota, US

File:Vivianite-Childrenite-117967.jpg

Vivianite and childrenite from the Siglo XX mine (tin mine in Bolivia)

File:Vivianite-141168.jpg

Vivianite from Bavaria (Germany)

File:Vivianite-Albite-265749.jpg

Vivianite and albite from Brazil

Vivianite (Template:Chem) is a hydrated iron(II) phosphate mineral found in a number of geological environments. Small amounts of manganese Mn²⁺, magnesium Mg²⁺, and calcium Ca²⁺ may substitute for iron Fe²⁺ in its structure.<ref name="Dana">Gaines et al (1997) Dana's New Mineralogy Eighth Edition. Wiley</ref> 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.<ref name=Atlasobs />

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.<ref>Although mindat.org claims "J. G. Vivian" is a typo for "J. H. Vivian", there is at least one reference that gives a full first name. The original description of Vivianite in Abraham Gottlob Werner, Letztes Mineral-System, Freiberg/Wien, 1817, p. 42 reads „Der Name ist vom Hrn. B. R. Werner zu Ehren des Hrn. J. Vivian aus Truro in Cornwall, dem Er die Kentnis des Fossils verdankt, gebildet.“ [“The name is formed by Mr. B. R. Werner in honour of Mr. J. Vivian from Truro in Cornwall, to whom he owes the memory of the fossil.”] It is ambiguous (and puzzling in its reference to B. R. Werner). As for Jeffrey G. Vivian, no other trace of him can be found in Google Books.</ref> Vivianite was discovered at Wheal Kind, in St Agnes, Cornwall.<ref name=Mindat />

Vivianite group

Vivianite group minerals have the general formula A₃(XO₄)₂·8H₂O, where A is a divalent metal cation and X is either phosphorus or arsenic, and they are monoclinic.<ref name=JRS9>Journal of the Russell Society (2006) 9:3</ref><ref>Template:Cite book</ref>

Group members are:

Mineral	Chemical formula	Crystal system
Annabergite	Ni3(AsO4)2·8H2O	Monoclinic
Arupite	Ni3(PO4)2·8H2O	Monoclinic
Baricite	(Mg2+,Fe2+)3(PO4)2·8H2O	Monoclinic
Erythrite	Co3(AsO4)2·8H2O	Monoclinic
Hörnesite	Mg3(AsO4)2·8H2O	Monoclinic
Köttigite	Zn3(AsO4)2·8H2O	Monoclinic
Manganohörnesite	(Mn2+,Mg)3(AsO4)2·8H2O	Monoclinic
Pakhomovskyite	Co3(PO4)2·8H2O	Monoclinic
Parasymplesite	Fe2+3(AsO4)2·8H2O	Monoclinic
Vivianite	Fe2+3(PO4)2·8H2O	Monoclinic

Related:

– Bobierrite: Mg₃(PO₄)₂·8H₂O

– Symplesite: Fe²⁺₃(AsO₄)₂·8H₂O

– Metaköttigite: Zn₃(AsO₄)₂·8H₂O

– Metavivianite: (Fe²⁺_{Template:Math},Fe³⁺_{Template:Mvar})(PO₄)₂(OH)_{Template:Mvar}·Template:MathH₂O.<ref name=Dana/>

Template:SpaceNote: Metavivianite, that vivianite readily alters to, is not a member of the vivianite group because it contains trivalent Fe³⁺ cations.

Structure

In pure end member vivianite all the iron is divalent, Fe²⁺, but there are two distinct sites in the structure that these ions can occupy. In the first site, the Fe²⁺ is surrounded by four water molecules and two oxygens, making an octahedral group. In the second site, the Fe²⁺ is surrounded by two water molecules and four oxygens, again making an octahedral group. The oxygens are part of the phosphate groups (PO₄³⁻), that are tetrahedral. The vivianite structure has chains of these octahedra and tetrahedra that form sheets perpendicular to the a-crystal axis. The sheets are held together by weak bonds, and that accounts for the perfect cleavage between them.<ref name=Dana/>

The crystals are monoclinic, class 2/m, space group C 2/m, with two formula units per unit cell (Z = 2). The approximate values of the unit cell parameters are:

a = 10.1 Å, b = 13.4 Å, c = 4.7 Å and β = 104.3°,

with slightly different values given by different sources:

a = 10.086 Å, b = 13.441 Å, c = 4.703 Å, β = 104.27°<ref name=Mindat/><ref name=Dana/>

a = 10.06 Å, b = 13.41 Å, c = 4.696 Å, β = 104.3°<ref name=Webmin/>

a = 10.034–10.086 Å, b= 13.434–13.441 Å, c= 4.687–4.714 Å, β = 102.65–104.27°<ref name=Handbook/>

a = 10.024(6) Å, b = 13.436(3) Å, c = 4.693(4) Å, β = 102.30(5)°<ref name=Iwama />

Appearance

The mineral may occur as crystals, or as masses or concretions.<ref name=Dana/> The crystals are usually prismatic parallel to the c-crystal axis, and flattened perpendicular to the b-axis. Equant crystals are rarer.<ref name=Handbook/><ref name=Mindat/><ref name=Dana/> They may also occur as stellate (star-shaped) groups, or encrustations with a bladed or fibrous structure.<ref name=Dana/> Unaltered specimens are colorless to very pale green, but they oxidize on exposure to light (and possibly also in situ) to blue, then darker green, brown, purple and purplish black. The streak is white, altering to dark blue or brown. Crystals are transparent to translucent with a vitreous luster, pearly on the cleavage surface, or dull and earthy.<ref name=Handbook/><ref name=Mindat/><ref name=Webmin/><ref name=Dana/>

Optical properties

Vivianite is biaxial (+) with refractive indices approximately:

n_α = 1.58, n_β = 1.6, n_γ = 1.6, but different sources give somewhat different values

n_α = 1.579, n_β = 1.602, n_γ = 1.637<ref name=Dana/>

n_α = 1.579–1.616, n_β = 1.602–1.656, n_γ = 1.629–1.675<ref name=Handbook/><ref name=Mindat/>

n_α = 1.58–1.626, n_β = 1.598–1.662, n_γ = 1.627–1.699<ref name=Webmin/>

Birefringence: δ = 0.050–0.059<ref name=Mindat/> or 0.0470–0.0730<ref name=Webmin/>

The refractive indices increase with increasing oxidation, the birefringence decreases, and the pleochroism on {010} becomes stronger.<ref name=Mindat/><ref name=Dana/>

The angle between the optic axes, 2V, has been measured as between 63° and 83.5°; it can also be calculated from the refractive indices, giving a value between 78° and 88°.<ref name=Mindat/><ref name=Webmin/> The dispersion of the optic axes is weak, with r<v,<ref name=Handbook/><ref name=Mindat/><ref name=Dana/> or non-existent.<ref name=Webmin/> Vivianite is pleochroic with X= blue, deep blue or indigo-blue; Y= pale yellowish green, pale bluish green or yellow-green; Z= pale yellowish green or olive-yellow. X is parallel to the b-crystal axis and Z is inclined to the c-crystal axis at an angle of 28.5°.<ref name=Handbook /><ref name=Mindat /><ref name=Dana/> It is not fluorescent.<ref name=Mindat /><ref name=Webmin />

Physical properties

Vivianite is a soft mineral, with Mohs hardness only Template:Frac to 2, and specific gravity 2.7. It splits easily, with perfect cleavage perpendicular to the b-crystal axis, due to the sheet-like structure of the mineral. It is sectile, with a fibrous fracture, and thin laminae parallel to the cleavage plane are flexible. It is easily soluble in acids.<ref name=Mindat/><ref name=Dana/> It has a melting point of Template:Convert,<ref name=Mindat/> it darkens in color in H₂O₂,<ref name=Mindat/> and is not radioactive.<ref name=Webmin/>

Geological setting

Vivianite is a secondary mineral found in a number of geologic environments: the oxidation zone of metal ore deposits, in granite pegmatites containing phosphate minerals, in clays and glauconitic sediments, and in recent alluvial deposits replacing organic material such as peat, lignite, bog iron ores and forest soils (all). Bones and teeth buried in peat bogs are sometimes replaced by vivianite.<ref name=Petrov/> Some authors say that it is particularly associated with gossan, but this is disputed by Petrov.<ref name=Petrov>{{#invoke:citation/CS1|citation |CitationClass=web }}</ref>

Associated minerals include metavivianite, ludlamite, pyrite, siderite and pyrrhotite.<ref name=Handbook/><ref name=Petrov/> Hydrothermal veins produce the best crystal specimens with the classic gemmy green color.<ref name=Petrov/>

The type locality is Wheal Kind (Wheal Kine), West Wheal Kitty group, St Agnes, St Agnes District, Cornwall, England.<ref name=Mindat/>

Photo-oxidation

Oxidation of vivianite is an internal process; no oxygen or water enters or leaves the mineral from the outside. A visible light photon knocks a proton out of a water molecule, leaving a hydroxide ion (OH⁻). In turn, a divalent iron Fe²⁺ loses an electron to become Fe³⁺, i.e., it is oxidized and balances the charge. This process starts when visible light falls on the vivianite, and it can occur within a few minutes, drastically changing the color of the mineral. Eventually, the vivianite changes to a new species, metavivianite Fe²⁺₂Fe³⁺(PO₄)₂(OH)·7H₂O, which usually occurs as paramorphs after vivianite.<ref>Alfredo Petrov, 2006 on Mindat</ref>

Pigment

Vivianite was known as a pigment since Roman times, but its use in oil painting was rather limited.<ref>Vivianite at ColourLex</ref> It has been found in Vermeer's The Procuress in the blue-grey parts of the carpet in the foreground.<ref>H. Stege, C. Tilenschi und A. Unger. Bekanntes und Unbekanntes – neue Untersuchungen zur Palette Vermeers auf dem Gemälde „Bei der Kupplerin“. In: Uta Neidhardt und Marlies Giebe (Ed.), Johannes Vermeer – Bei der Kupplerin, Ausstellungskatalog Dresden 2004, pp. 76–82.</ref>

File:Jan Vermeer van Delft 002.jpg

Johannes Vermeer, The Procuress, 1656

Localities

• Brazil. Cigana Mine, Galileia, Minas Gerais, with muscovite and pyrite.<ref name=Minrec35-2>The Mineralogical Record (2004) 35-2:156</ref> Typically wedge-shaped crystals of vivianite to 11 cm across, of medium lustre, smoke-blue color and good transparency on matrix of sharp silvery muscovite plates, some with druses of pyrite microcrystals.<ref name=Minrec35-3>The Mineralogical Record (2004) 35-3:252</ref>
• Bolivia: Llallagua, Potosi: Crystals to 10 cm at the Siglio XX mine.<ref name=Dana/> Transparent bottle-green crystals to 10 cm from the San Jose/San Firmin vein. In general, the vivianite occurs as prismatic crystals on a matrix of botryoidal goethite derived from the alteration of pyrite and marcasite. Specimens found in 2000 were associated with childrenite, cronstedtite, pyrrhotite, franckeite and pink massive sphalerite.<ref name=Minrec37>The Mineralogical Record (2006) 37-2:156</ref>
• Cameroon: The world's largest vivianite crystals (more than a meter long) from mud.<ref name=Petrov/>
• Canada: In bog iron at Côte St Charles, Vaudreuil-Soulanges, Montérégie, Québec.<ref name=Dana/>
• Germany: In the limonite ores in Amberg-Auerbach and in the pegmatites of Hagendorf, Bavaria.<ref name=Dana/>
• Japan: At Nagasawa, Iwama-machi, Ibaraki Prefecture, vivianite was found along fractures in rocks rich in graphite, pyrite and pyrrhotite. The vivianite is intimately associated with pyrite and occurs as very thin tabular crystals, up to 10 cm in length.<ref name=Iwama />
• Kosovo. Trepča Mines, Stari Trg. Thick prismatic crystals up to 10 cm long and 2 cm thick, relatively stable. Deep green in color and transparent, commonly resting on pyrrhotite or pyrite, and in some cases on quartz or carbonates.<ref name=Minrec38>The Mineralogical Record (2007) 38-4:290</ref>
• Mexico: In blue-green gem quality crystals to 8 cm at the San Antonio Mine, Santa Eulalia, Chihuahua.<ref name=Dana/>
• Russia: In sedimentary stratified iron ore deposits on the Taman peninsula on the Black Sea.<ref name=Dana/><ref name=":0">Template:Cite book</ref>
• Slovenia: In Idrija mine, 2 mm bluish vivianite crystals in fissures of Langobardian sandstone were found.<ref>Template:Cite book</ref>
• Spain: At the Brunita mine, Cartagena, Murcia, vivianite was found as deep green crystals, up to 8 cm<ref>Template:Cite book</ref>
• Ukraine: In the Kerch iron ore basin in the Crimean Peninsula,<ref name=":0" /> peatlands of Volyn' region <ref name=":1">Template:Cite book</ref> and Zakarpattia region.<ref name=":1" />
• US: In diatomite in a tertiary lake bed near Burey, Shasta County, California.<ref name=Dana/>
• US: In green sand at Middletown, New Castle County, Delaware.<ref name=Dana/>
• US: Blackbird Mine, Lemhi County, Idaho. Crystals in shades of pink, green, greyish blue, purple and purplish black, as well as colorless. The unique deep purple color of some Blackbird mine specimens is characteristic of the locality. Some single crystals have both purple and green zones. Vivianite crystals from the Blackbird Mine are usually elongated and blade-like. They occur as singles and groups on dark altered schist and on white quartz. Associated minerals include ludlamite, quartz and siderite.<ref name=Minrec41>The Mineralogical Record (2010) 41-4:366</ref>
• US: Abundant in the pegmatites of Newry, Maine.<ref name=Dana/>
• New Zealand: Small amounts of vivianite are present within the sediments of Lake Kohangapiripiri.<ref>Cochran, U., Goff, J., Hannah, M., and Hull, A. (1999) Relative stability on a tectonically active coast: paleoenvironment during the last 7000 years at Lake Kohangapiripiri, Wellington, New Zealand, Quaternary International, 56, 53–63</ref>

See also

• List of minerals
• List of minerals named after people

External links

• Vivianite as a pigment at ColourLex