Minerals vivianite

Figure 9 A Fe -Fe intervalence charge-transfer band in the mineral vivianite, Fe3 (P04)3-8H20 upon oxidation. (Ref. 22. Reproduced by permission of Kluwer Academic Publishers)...

This is an extremely rare fossilised mammoth ivory that originated in southern France. For many years it was thought to have been stained blue naturally by the presence of the mineral vivianite in the surrounding soil. However, it is now believed that the ivory was deliberately heat-treated in the Middle Ages, to resemble the mineral turquoise. It is easily mistaken for turquoise, but close inspection reveals the typical dentine patterning of mammoth tusk. Today odontolite is only seen in museums or private collections. 

Phosphates Apatite, crandallite-group minerals, vivianite Apatite... 

Rose (1916) states HaaXElsenblau ( ironblue ) mdBlaueisenerde ( blue iron earth ) were terms for the iron phosphate mineral, vivianite (q.v.). 

Cobalt arsenate may also be referred to as the anhydrous synthetic vivianite arsenate of cobalt because the compound is related to the naturally occurring mineral vivianite, Fe3(P04)2-8H20 (. v.), where cobalt may substitnte for iron, and arsenic for phosphorous. The hydrated equivalent of cobalt arsenate is the mineral erythrite (. v.) and synthetic analognes (Martens et al., 2003a). 

Native Prussian blue was used synonymously with terms such as blue iron earth and blue ochre (qq.v.). It may be equated to the mineral vivianite (q.v.), an iron phosphate hydrate. Salter (1869) writes In name, there is also another variety of this pigment, known as Native Prussian Blue which is really a native phosphate of iron, occurring as a blue earthy powder, or as a white powder which becomes blue by exposure. ... 

Field (1835) described a mineral colour called blue ochre of rare occurrence found in Cornwall, and also in North America which he expressed as being a sub-phosphate of iron , the second edition (1841) adding that it is found with iron pyrites Field is clearly referring here to the mineral vivianite. Harley (1982) states that this colour is mentioned in late eighteenth and early nineteenth English sources. 

Since ferrous iron usually colors minerals green, and ferric iron yellow or brown, it may seem rather remarkable that the presence of both together should give rise to a blue color, as in the case of vivianite. It may be pointed out, however, that this is by no means a unique instance of such an effect. Even apart from the artificial substances, Prussian and Turnbull s blues, which are complex cyanides containing both ferric and ferrous iron, there are several blue minerals in which the color seems explainable only on this basis. The most noteworthy of these are crocidolite and related amphiboles iolite and the blue tourmaline or indicolite. Other instances may perhaps be discovered, should this subject ever be investigated as it deserves to be . 

Phosphate is remineralized during the oxidation of organic matter and dissolution of hard parts, such as bones and teeth, that are composed of the minerals hydroxyapatite and fluoroapatite. Unlike the other products of remineralization, pore-water phosphate concentrations are regulated only by mineral solubility, such as through vivianite (iron phosphate) and francolite (carbonate fluoroapatite). Redox reactions are not significant because phosphorus exists nearly entirely in the h-5 oxidation state. 

The affinity between the tetrahedrally arranged orthophosphate oxyanion, P04, and hexava-lently coordinated metal cations lends itself to a classification of phosphate minerals in a scheme similar to silicates (SiO -) framework, insular, chain, and layer phosphates. Examples of this scheme, advanced by Povarennykh (1972) and further elaborated by Lindsay Vlek (1977), include berlinite (AIPO4 framework) hydroxyapatite (insular) monetite (CaHP04, chain) and vivianite (Fe4(P04)2-2H2O, layer). 

Ferrous orthoarsenate occurs naturally as the mineral symplesite (see p. 16), which is the octahydrate, Fe3(As04)2.8H20. This is found in pale blue or green prismatic or tabular crystals, probably isomorphous with vivianite and having axial ratios 5 a b c = 0-7806 1 0-6812, and 3 = 72° 43. The mineral is decomposed by caustic alkali with formation of ferric hydroxide.6... 

Since ferrous iron usually colors minerals green, and ferric iron yellow or brown, it may seem rather remarkable that the presence of both together should give rise to a blue color, as in the case of vivianite. — Other instances may perhaps be discovered, should this subject ever be investigated as it deserves to be. 

Vivianite, Fe2+3(P04)2.8H20, is the classic example of a mineral showing an intervalence charge transfer transition (Wherry, 1918 Bums, 1981). Vivianite has a diagnostic indigo-blue colour and a well characterized Fe2+ —> Fe3+ IVCT absorption band in the polarized spectra illustrated in fig. 4.12 and is the datum with which electron interaction parameters for other minerals are compared. The chemical formula of vivianite is not indicative of a mixed-valence compound. However, the pale-green colour of newly cleaved vivianite crystals or fleshly... 

Just as vivianite is regarded as the simplest example of a mineral with isolated clusters of Fe2+-Fe3+ octahedra showing IVCT transitions, so too is magnetite considered to be the classic example of a structure-type with infinite chains of Fe2+ -Fe3+ octahedra exhibiting electron delocalization. Magnetite, Fe304 or Fe2+Fe3+204, has the spinel structure illustrated in fig. 4.18 with an inverse cation distribution ( 6.4). Thus, half the Fe3+ ions occupy isolated tetrahedral sites,... 

Faye, G. H. (1968b) The optical absorption spectra of iron in six-coordinate sites in chlorite, biotite, phlogopite and vivianite. Some aspects of pleochroism in the sheet silicates. Canad. Mineral., 9,403-25. 

Faye, G. H., Manning, P. G. Nickel, E. H. (1968) The polarized optical absorption spectra of tourmaline, cordierite, chloritoid, and vivianite ferrous-ferric electronic interaction as a source of pleochroism. Amer. Mineral., 53, 1174—201. 

McCammon, C. A. Bums, R. G. (1980) The oxidation mechanism of vivianite as studied by Mossbauer spectroscopy. Amer. Mineral., 65, 361-6. 

Watson, T. L. (1918) The color change in vivianite and its effect on the optical properties. Amer. Mineral., 3, 159-61. 

Sedimentary pools of P have generally been divided into the following fractions (1) organic P, (2) Fe bound P, (3) authigenic P minerals (e.g., CFA, struvite, and vivianite), and (4) detrital P minerals (e.g., feldspar). 

Vivianite Some iron (copper and tin) ores and as earthy mineral. Fe3(P04)2.8H20 Monoelinie 2-6-2-7... 

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