vivianite-metavivianite-kerchenite

interested in obtaining small quanties of these minerals for analysis by vibrational spectroscopy.
interested in studing Fe2+/Fe3+ ratios.
Any assistance greatly appreciated

Hello Ray,

I have some vivianite from a pegmatite in Maine.
It is micro material, altered from triphylite.
If this is suitable for your studies, send me an address (off line) and I'll mail a couple pieces to you.

Dick

Here we have studied the Fe2+/Fe3+ of ironsandstone all over Belgium, must say the results where asthonishing. In a few months a new search must start , I am looking for vivianite in river beds here in Begium, to determine the ironrate.

greets
Philip

Are you including santabarbaraite in that list? Although I think all the iron in it is considered Fe3+.

Hello,
As promised I will give you the moethod we used...

First you use H2SO4 to Solve the iron present in Fe2+ and Fe 3+ ions, because
Fe2O3+3H2SO4 => Fe2(SO4)3 + 3 H2O
FeO + H2SO4 => FeSo4 + H2O
We have H2O environment that can solve de ironbonds and part it up in ions.

Second Fe3+ is reduced to Fe3+ by adding acid and Sn powder. The acid and the Sn powder will react and form Zn + 2H(+) --> Zn(2+) + H2 and 2Fe(3+) + H2 --> 2 Fe(2+) + 2H(+)

We have only Fe (2+) ions now, with a titration with K2Mn2O7, reaction: MnO4 (-) + 8H(+) + 5 Fe (2+) --> Mn (2+) + 4H2O+5Fe(3+). You see, when te colur changes. Write down the ml of K2Mn2O7

Then M= 1.00 *10 ^ (-2) Mol/l
Then you take the average ml titrated
n= M* average * 10^(-3) => X
Fe= 55.85 g/mol => X* 55.85*10 ==> Y(gramm)

100* Y / Total gramms of material you took, then you have the percent. That is the best I can explain.

I hope it is of any use
Greets
Philip

As Jim Ferraiolo has commented above, this is a complicated series with potentially a lot of different minerals that should be investigated along with vivianite and metavivianite.

The oxidation of the primary ferrous phosphate, vivianite, Fe3(PO4)2·8H2O yields a cascade of products spanning the redox conditions applying to vivianite and the redox conditions applying to the fully oxidized state. Initially, the oxidation of vivianite leads to Fe(II)3-x Fe(III)x(PO4)2(OH)x·(8-x)H2O, in which the monoclinic crystal structure is preserved up to x 1.2, and overall charge balance is conserved by converting some of the water of crystallization to hydroxyl anions. Oxidation past x 1.4 apparently can lead first to a triclinic structure with the same charge-compensated formula, Fe(II)3-x Fe(III)x(PO4)2(OH)x·(8-x)H2O as vivianite. At present, only this triclinic phase, according to Rodgers 1986, is correctly denoted as metavivianite, which is now known to be a misnomer since vivianite and metavivianite are not dimorphous, but differ compositionally (i.e., there is no phase transition connecting these forms). The name kerchenite may have priority in its application to this triclinic phase; however, this is far from settled.

The named mineral, ferrostrunzite, Fe2+Fe3+2(PO4)2(OH)2·6H2O, seems to correspond to the x = 2 composition of triclinic metavivianite. The named mineral, ferristrunzite, Fe3+Fe3+2(PO4)2(OH)3·6H2O , would seem to correspond to the x=3 composition of triclinic metavivianite; however, metavivianite oxidized to this extent seems to pass into an amorphous phase first (perhaps to be identified with the newly named, amorphous santabarbaraite).

There are several other issues concerning the vivianite-metavivianite oxidation pathway that have not been fully resolved. Oxidation of vivianite can seemingly occur in at least two ways:

1. self-oxidation, involving the internal hydrolysis reaction Fe+2-H2O Fe+3-OH- + ½H2 with the hydrogen diffusing out of the crystal (occurs during heating in vacuum), and

2. oxidation by O2 diffusing into the crystal (occurs during grinding in air).

No complete investigation of photo-oxidation (or photo-enhancement of self-oxidation) seems to have been performed so far. This is of more than casual interest because of the possibility of vivianite altering even as it is being studied in the X-ray beam. This may also have bearing on any attempts to determine the iron oxidation state by XPS.

At any rate, Dr. Frost and his co-workers have their work cut out for him deciphering the relationships in this complex group of materials. The initial paper in this work is Frost et al., 2002. Raman and Infrared Spectroscopic Study of the Vivianite-group Phosphates vivianite, baricite and bobierrite. Min. Mag. 66(6):1063-1073.

Non-destructive spectroscopic methods are the way to go to determine Fe2+ in vivianite. Wet chemical methods have the defect that fine grinding of minerals results in partial oxidation of Fe2+, and further oxidation can occur in solution. Measurable oxidation of Fe2+ even occurs during fine grinding of tough silicates like tourmaline, so I don't trust any chemical analyses of Fe2+.

The santabarbaraite paper considers the vivianite oxidation to go from vivianite (monoclinic) to metavivianite (triclinic) to santabarbaraite (amorphous), or from ferrous to ferric-ferrous to ferric.

Kerchenite (kertschenite/oxykertschenite) nomenclature is also discussed in the paper. Kertschenite and oxykerschenite have been used mostly to describe oxidized vivianite, but Dana 8 uses them as a synonym for metavivanite. The opinion is "clear that kertschenite and oxykertchenite have never been suffuciently characterized." "Therefore a different name was required to identify the amorphous ferric hydroxy phosphate hydrate."

Finally, to offset questions about an amorphous phase being accepted, that is also discussed in the paper. An amorphous phase can be accepted as a new mineral provided that complete quantitative chemical analyses and spectroscopic data are available to demonstrate the uniqueness of the phase. (IMA guidelines).

In addition to the type locality in Italy, santabarbaraite has recently been confirmed as pseudomorphs after vivianite from the abandoned "Quarry A", Kamysh-Burun Iron Deposit, Kerch, Ukraine. Remarkably attractive stuff, but very little of it was collected.

Tony

The origin of some of the samples used in the Moessbauer studies are of interest because they cover some of the famous sites for vivianite and metavivianite. Some of the site names and spellings may need up-dating to current usage. No one seems to have studied the Bingham, UT material.

Vivianite, Fe(II)3-xFe(III)x(PO4)2(OH)x·(8-x)H2O, 0 < x < 1.2 , Monoclinic

Natural Vivianite, N'Gaoundere, Cameroon; Gonser and Grant, 1967

Natural Vivianite, Anlona (sic), N'Gounderé, Cameroon; Mattievich and Danon, 1977

Oxidized Natural Vivianite, Anluoa, Cameroon; x = 0.12; Dormann and Poullen, 1980

Natural Vivianite, Llallagua, Bolivia; x = 0.12; Rodgers et al., 1993

Oxidized Natural Vivianite, Llallagua, Bolivia; x = 0.33; McCammon and Burns, 1980

Natural Vivianite, Llallagua, Bolivia; x = 0.48; Rodgers et al., 1993

Oxidized Natural Vivianite, Mullica Hill, NJ; x = 0.51; Dormann and Poullen, 1980

Oxidized Natural Vivianite, Llallagua, Bolivia; x = 0.51; McCammon and Burns, 1980

Vivianite from Blue Nodule, Lago Maggiore, Italy; x = 0.84; Nembrini et al., 1983

Oxidized Natural Vivianite, Llallagua, Bolivia; x = 0.93; McCammon and Burns, 1980

Oxidized Natural Vivianite, Llallagua, Bolivia; x = 1.02; McCammon and Burns, 1980

Oxidized Natural Vivianite, Kamisch-Burun, USSR; x = 1.11; Dormann and Poullen, 1980

Oxidized Natural Vivianite, Llallagua, Bolivia; x = 1.11; McCammon and Burns, 1980

Oxidized Natural Vivianite, Mullica Hill, NJ; x = 1.15; Amthauer and Rossman, 1984

Metavivianite, Fe(II)3-xFe(III)x(PO4)2(OH)x·(8-x)H2O, 1.4 < x < 3 , Triclinic

Natural Metavivianite, Cornwall, England; x = 1.62; Dormann and Poullen, 1980

Natural Metavivianite, Big Chief pegmatite, SD; x = 1.86; Rodgers and Johnston, 1985

Natural Metavivianite, Ibex Mine, Colorado; x = 1.95; Dormann and Poullen, 1980

Natural Metavivianite, Kamisch-Burun, USSR; x = 2.46; Dormann and Poullen, 1980

Metavivianite from Orange Nodule, Lago Maggiore, Italy, x = 2.58, Nembrini et al., 1983

Natural Metavivianite, Yukon, Canada; x = 2.91; Dormann and Poullen, 1980


References

Amthauer, G., and Rossman, G.R., 1984, Mixed Valence of Iron in Minerals with Cation Clusters, Phys. Chem. Miner. v. 11(1), p. 37-51

Dormann, J.L. and Poullen, J.F., 1980, Etude par Specroscopie Mössbauer de Vivianites oxydées naturelles, Bull. Minéral. v. 103(6), p. 633-639.

Gonser, U., and Grant, R.W., 1967, Determination of Spin Directions and Electric Field Gradient Axes in Vivianite by Polarized Recoil Free -Rays, Phys. Stat. Solidi v. 21, p. 331-342.

McCammon, C.A., and Burns, R.G., 1980, The Oxidation Mechanism of Vivianite as studied by Mössbauer Spectroscopy , Am. Mineral. v. 65(3-4), p. 361-366.

Nembrini, G.P., Capobianco, J.A., Viel, M., and Williams, A.F., 1983, A Mössbauer and Chemical Study of the Formation of Vivianite in Sediments of Lago Maggiore (Italy), Geochim. Cosmochim. Acta v. 47, p. 1459-1464.

Rodgers, K.A., and Johnston, J.H., 1985, Type Metavivianite: Mössbauer Evidence for a Revised Composition, Neues Jahrb. Mineral., Monatsh. v. (12), 539-542.

Rodgers, K.A., Kobe, H.W., and Childs, C. W., 1993, Characterization of Vivianite from Catavi, Llallagua, Bolivia, Mineral. Petrol. v. 47(2-4), p. 193-208.