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Vivianite
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
General
Category	Phosphate mineral Vivianite group
Formula (repeating unit)	Fe 3(PO 4) 2·8H 2O
IMA symbol	Viv
Strunz classification	8.CE.40 (10 ed) 7/C.13-40 (8 ed)
Dana classification	40.3.6.1
Crystal system	Monoclinic
Crystal class	Prismatic (2/m) (same H-M symbol)
Space group	C2/m
Unit cell	a = 10.086 Å, b = 13.441 Å c = 4.703 Å; β = 104.27°; Z = 2
Identification
Formula mass	501.61 g/mol
Color	Colorless, very pale green, becoming dark blue, dark greenish blue, indigo-blue, then black with oxidation
Crystal 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 scale hardness	1.5–2
Luster	Vitreous, pearly on the cleavage, dull when earthy
Streak	White, altering to dark blue, brown
Diaphaneity	Transparent to translucent
Specific gravity	2.68
Optical properties	Biaxial (+); moderate relief
Refractive index	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 angle	Measured: 63° to 83.5°, Calculated: 78° to 88°
Dispersion	r < v, weak
Ultraviolet fluorescence	Not fluorescent
Melting point	1,114 °C (2,037 °F)
Solubility	Easily soluble in acids
Alters to	Metavivianite
References

Vivianite (Fe
₃(PO
₄)
₂·8H
₂O) is a hydrated iron(II) phosphate mineral found in a number of geological environments. Small amounts of manganese Mn, magnesium Mg, and calcium Ca may substitute for iron Fe 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.

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.

Group members are:

Related:

– Bobierrite: Mg₃(PO₄)₂·8H₂O

– Symplesite: Fe₃(AsO₄)₂·8H₂O

– Metaköttigite: Zn₃(AsO₄)₂·8H₂O

– Metavivianite: (Fe_3−x,Fe_x)(PO₄)₂(OH)_x·(8-x)H₂O.

   Note: Metavivianite, that vivianite readily alters to, is not a member of the vivianite group because it contains trivalent Fe cations.

Structure

In pure end member vivianite all the iron is divalent, Fe, but there are two distinct sites in the structure that these ions can occupy. In the first site, the Fe is surrounded by four water molecules and two oxygens, making an octahedral group. In the second site, the Fe is surrounded by two water molecules and four oxygens, again making an octahedral group. The oxygens are part of the phosphate groups (PO₄), 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.

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°

a = 10.06 Å, b = 13.41 Å, c = 4.696 Å, β = 104.3°

a = 10.034–10.086 Å, b= 13.434–13.441 Å, c= 4.687–4.714 Å, β = 102.65–104.27°

a = 10.024(6) Å, b = 13.436(3) Å, c = 4.693(4) Å, β = 102.30(5)°

Appearance

The mineral may occur as crystals, or as masses or concretions. The crystals are usually prismatic parallel to the c-crystal axis, and flattened perpendicular to the b-axis. Equant crystals are rarer. They may also occur as stellate (star-shaped) groups, or encrustations with a bladed or fibrous structure. 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.

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

n_α = 1.579–1.616, n_β = 1.602–1.656, n_γ = 1.629–1.675

n_α = 1.58–1.626, n_β = 1.598–1.662, n_γ = 1.627–1.699

Birefringence: δ = 0.050–0.059 or 0.0470–0.0730

The refractive indices increase with increasing oxidation, the birefringence decreases, and the pleochroism on {010} becomes stronger.

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°. The dispersion of the optic axes is weak, with r<v, or non-existent. 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°. It is not fluorescent.

Physical properties

Vivianite is a soft mineral, with Mohs hardness only 1+1⁄2 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. It has a melting point of 1,114 °C (2,037 °F), it darkens in color in H₂O₂, and is not radioactive.

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. Some authors say that it is particularly associated with gossan, but this is disputed by Petrov.

Associated minerals include metavivianite, ludlamite, pyrite, siderite and pyrrhotite. Hydrothermal veins produce the best crystal specimens with the classic gemmy green color.

The type locality is Wheal Kind (Wheal Kine), West Wheal Kitty group, St Agnes, St Agnes District, Cornwall, England.

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 Fe loses an electron to become Fe, 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 Fe₂Fe(PO₄)₂(OH)·7H₂O, which usually occurs as paramorphs after vivianite.

Pigment

Vivianite was known as a pigment since Roman times, but its use in oil painting was rather limited. It has been found in Vermeer's The Procuress in the blue-grey parts of the carpet in the foreground.

Localities

• Brazil. Cigana Mine, Galileia, Minas Gerais, with muscovite and pyrite. 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.
• Bolivia: Llallagua, Potosi: Crystals to 10 cm at the Siglio XX mine. 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.
• Cameroon: The world's largest vivianite crystals (more than a meter long) from mud.
• Canada: In bog iron at Côte St Charles, Vaudreuil-Soulanges, Montérégie, Québec.
• Germany: In the limonite ores in Amberg-Auerbach and in the pegmatites of Hagendorf, Bavaria.
• 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.
• 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.
• Mexico: In blue-green gem quality crystals to 8 cm at the San Antonio Mine, Santa Eulalia, Chihuahua.
• Russia: In sedimentary stratified iron ore deposits on the Taman peninsula on the Black Sea.
• Spain: At the Brunita mine, Cartagena, Murcia, vivianite was found as deep green crystals, up to 8 cm
• Ukraine: In the Kerch iron ore basin in the Crimean Peninsula, peatlands of Volyn' region and Zakarpattia region.
• US: In diatomite in a tertiary lake bed near Burey, Shasta County, California.
• US: In green sand at Middletown, New Castle County, Delaware.
• 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.
• US: Abundant in the pegmatites of Newry, Maine.
• New Zealand: Small amounts of vivianite are present within the sediments of Lake Kohangapiripiri.

See also

• List of minerals
• List of minerals named after people

References

1. Warr, L.N. (2021). "IMA–CNMNC approved mineral symbols". Mineralogical Magazine. 85 (3): 291–320. Bibcode:2021MinM...85..291W. doi:10.1180/mgm.2021.43. S2CID 235729616.
2. ^ John W. Anthony; Richard A. Bideaux; Kenneth W. Bladh & Monte C. Nichols (2005). "Handbook of Mineralogy" (PDF). Chantilly, VA, USA: Mineralogical Society of America.
3. ^ Vivianite (Mindat.org)
4. ^ Webmineral data
5. ^ Gaines et al (1997) Dana's New Mineralogy Eighth Edition. Wiley
6. The Vivid Blue Mineral That Grows on Buried Bodies and Confuses Archaeologists
7. 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.“ 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.
8. Journal of the Russell Society (2006) 9:3
9. Back, Malcolm E. (2014). Fleischer's Glossary of Mineral Species (11 ed.). Tucson AZ: Mineralogical Record Inc. p. 434.
10. ^ Banno Yasuyuki; Bunno Michiaki; Haruna Makoto & Kono Masahide (1999). "Vivianite from Nagasawa, Iwama-machi, Ibaraki Prefecture, Japan. New finding from meta-pelitic rocks". Bulletin of the Geological Survey of Japan (in Japanese). 50 (2): 117–121. ISSN 0016-7665. Archived from the original on 2012-02-29. Retrieved 2008-03-20.
11. ^ Petrov, Alfredo (1 January 2008). "Alfredo Petrov – A Scientific Study of the Absorption of Evil by Vivianite". Mindat.org. Retrieved 23 September 2018.
12. Alfredo Petrov, 2006 on Mindat
13. Vivianite at ColourLex
14. 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.
15. The Mineralogical Record (2004) 35-2:156
16. The Mineralogical Record (2004) 35-3:252
17. The Mineralogical Record (2006) 37-2:156
18. The Mineralogical Record (2007) 38-4:290
19. ^ Handbook of mineralogy. 4: Arsenates, Phosphates, vanadates. Tucson, Ariz: Mineral Data Publ. 2000. p. 632. ISBN 978-0-9622097-3-4.
20. Calvo, Miguel (2015). Minerales y Minas de España. Fosfatos, Arseniatos y Vanadatos. Escuela Técnica Superior de Ingenieros de Minas de Madrid. Fundación Gómez Pardo. Madrid, Spain. p. 297. ISBN 978-84-95063-96-0.
21. ^ Білецький, Володимир; Суярко, Василь; Іщенко, Лілія (2018). Мінералого-петрографічний словник. Книга перша. Мінералогічний словник [Mineralogy dictionary]. Харків: НТУ «ХПІ». pp. 26–27. ISBN 978-617-7565-14-6.
22. The Mineralogical Record (2010) 41-4:366
23. 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

External links

• Vivianite as a pigment at ColourLex

• Iron(II) minerals
• Phosphate minerals
• Monoclinic minerals
• Minerals in space group 10
• Vivianite group
• Minerals described in 1817