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See detailA structural, magnetic, and Mossbauer spectral study of several Na-Mn-Fe-bearing alluaudites
Hatert, Frédéric ULg; Long, G. J.; Hautot, D. et al

in Physics and Chemistry of Minerals (2004), 31(8), 487-506

The synthesis and the chemical, structural, magnetic, and Mossbauer spectral characterization of three synthetic alluaudites, Na2Mn2Fe(PO4)(3), NaMn Fe-2(PO4)(3) and (Na2MnFeFeIII)-Fe-II(PO4)(3), and a ... [more ▼]

The synthesis and the chemical, structural, magnetic, and Mossbauer spectral characterization of three synthetic alluaudites, Na2Mn2Fe(PO4)(3), NaMn Fe-2(PO4)(3) and (Na2MnFeFeIII)-Fe-II(PO4)(3), and a natural sample with the nominal composition of NaMn Fe-2(PO4)(3), collected in the Buranga pegmatite, Rwanda, are reported. All four compounds have the expected alluaudite monoclinic C2/c structure with the general formula [A(2)A(2)'][A(1)A(1)'A(1)(2)'']M(1)M(2)(2)(PO4)(3) in which manganese(II) is on the M(1) site and manganese(II), iron(III) and, in some cases, iron(II) on the M(2) site. The X-ray structure of Na2Mn2Fe(PO4)(3) also indicates a partially disordered distribution of Na-I and Mn-II on the M(1) and A(1) crystallographic sites. All four compounds are paramagnetic above 40 K and antiferromagnetically ordered below. Above 40 K the effective magnetic moments of NaMnFe2(PO4)(3) and Na2MnFeII Fe-III(PO4)(3) are those expected of high-spin manganese(II) and iron(III) with the (6)A(1g) electronic ground state and high-spin iron(II) with the T-5(2g) electronic ground state. In contrast, the effective magnetic moment of Na2Mn2Fe(PO4)(3) is lower than expected as a result of enhanced antiferromagnetic exchange coupling by the manganese(II) on the M(2) site. The Mossbauer spectra of all four compounds have been measured from 4.2 to 295 K and have been found to be magnetically ordered below 40 K for Na2Mn2Fe(PO4)(3) and similar to35 K for the remaining compounds. The Mossbauer spectra of Na2Mn2Fe(PO4)(3) exhibit the two expected iron(III) quadrupole doublets and/or magnetic sextets expected for a random distribution of manganese(II) and iron(III) ions on the M(2) site. Further, the Mossbauer spectra of (Na2MnFeFeIII)-Fe-II(PO4)(3) exhibit the two iron(II) and two iron(III) quadrupole doublets and/or magnetic sextets expected for a random distribution of iron(II) and iron(III) on the M(2) site. Surprisingly, the synthetic and natural samples of NaMnFe2(PO4)(3) have 19 and 10% of iron(II) on the M(2) site; apparently the presence of some iron(II) stabilizes the alluaudite structure through the reduction of iron(III)-iron(III) repulsion. The temperature dependence of the iron(II) quadrupole splitting yields a 440 to 600 cm(-1) low-symmetry component to the octahedral crystal field splitting at the M(2) site. The iron(II) and iron(III) hyperfine fields observed at 4.2 K are consistent with the presence of antiferromagnetic ordering at low temperatures in all four compounds. [less ▲]

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See detailPetrographic evidence for primary hagendorfite in an unusual assemblage of phosphate minerals, Kibingo granitic pegmatite, Rwanda
Fransolet, André-Mathieu ULg; Hatert, Frédéric ULg; Fontan, François

in Canadian Mineralogist (2004), 42(Part 3), 697-704

A sample from the Kibingo granitic pegmatite, Rwanda, shows a striking assemblage of an alluaudite-group mineral with heterosite. The core of alluaudite s.l. is strongly pleochroic in blue green to ... [more ▼]

A sample from the Kibingo granitic pegmatite, Rwanda, shows a striking assemblage of an alluaudite-group mineral with heterosite. The core of alluaudite s.l. is strongly pleochroic in blue green to pinkish grey hues, and is rimmed by an irregular border, weakly pleochroic in yellow brown to greenish yellow tints. The pleochroic core is very rich in Na (up to 9.35% Na2O), whereas the yellowish green border is depleted in Na (3.75% Na2O) and more oxidized. The decrease of the Na contents is not accompanied by significant variations of the ratio Fe-tot/(Fe-tot + Mn). This mechanism represents the progressive transition of hagendorfite to alluaudite sensu stricto, and results from an oxidation, Na+ + Fe2+ --> rectangle + Fe3+. Heterosite exhibits cracks that are parallel to one of the cleavage directions, and that are favorable to the development of a product of alteration, identified as cyrilovite. Heterosite shows a chemical composition close to the idealized formula (Fe0.853+Mn0.153+)PO4, with a Mg content constant and quite low, i.e., 0.023 Mg apfu. The Kibingo heterosite seems to be the Fe-richest member known so far. The heterosite corresponds to an oxidized Fe-rich member of the triphylite - lithiophilite series, a member that was initially in equilibrium with the primary hagendorfite. The ratio Fe-tot/(Fe-tot + Mn) of the two minerals of this assemblage is different: the value is about 0.70 ire hagendorfite, and 0.85 in the former triphylite. The temperature of formation of hagendorfite is estimated at about 600degreesC. Contrary to the information in the literature, the Kibingo pegmatitic body differs from the amblygonite pegmatite of Mwaka and could be a poorly evolved neighboring pegmatitic lens. [less ▲]

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See detailPreliminary data on the crystal chemitry of synthetic fillowite-type phosphates
Hatert, Frédéric ULg; Fransolet, André-Mathieu ULg

in Berichte der Deutschen Mineralogischen Gesellschaft : Beihefte zum European Journal of Mineralogy (2003), 15

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See detailAn X-ray Rietveld, infrared, and Mossbauer spectral study of the NaMn(Fe1-xInx)(2)(PO4)(3) alluaudite-type solid solution
Hatert, Frédéric ULg; Hermann, Raphaël ULg; Long, Gary J. et al

in American Mineralogist (2003), 88(1), 211-222

Several compounds of the NaMn(Fe1-xInx)(2)(PO4)(3) solid solution were synthesized by solid state reaction in air; pure alluaudite-like compounds were obtained for x = 0.00 to 1.00. X-ray Rietveld ... [more ▼]

Several compounds of the NaMn(Fe1-xInx)(2)(PO4)(3) solid solution were synthesized by solid state reaction in air; pure alluaudite-like compounds were obtained for x = 0.00 to 1.00. X-ray Rietveld refinements indicate the presence of Na+ at the A1 and A2' sites, Mn2+ at the M1 site, and Fe2+, Fe3+, and In3+ at the M2 site. The presence of small amounts of In3+ at the M I site, and Mn2+ at the M2 site, indicates a partially disordered distribution between these cations. A good correlation was also established between the M1-M2 bond distance and the beta angle of the alluaudite-like compounds. The disordered distribution of Fe2+, Fe3+, and In3+ at the M2 site is confirmed by the broadness of the infrared absorption bands. The Mossbauer spectra, measured between 90 and 295 K, were analyzed in terms of a model that takes into account the next-nearest neighbor interactions around the M2 crystallographic site. In all cases these spectra reveal the unexpected presence of small amounts of Fe2+ at the M2 site, an amount that decreases as the In3+ content increases. The Fe2+ and Fe3+ isomer shifts are typical of the alluaudite structure and vary with temperature, as expected from a second-order Doppler shift. The derived iron vibrating masses and Mossbauer lattice temperatures are within the expected range of values for iron cations in an octahedral environment. The Fe2+ and Fe3+ quadrupole splittings are also typical of the alluaudite structure and the temperature dependence of the Fe2+ quadrupole splitting was fit with the model of Ingalls (1964), which yielded a ground state orbital splitting of ca. 380 to 570 cm(-1) for the Fe2+ sites. [less ▲]

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See detailGraulichite-(Ce), a new arsenate mineral from the Stavelot Massif, Belgium
Hatert, Frédéric ULg; Pasero, Marco; Fransolet, André-Mathieu ULg et al

in European Journal of Mineralogy (2003), 15(4, JUL-AUG), 733-739

Graulichite-(Ce), ideally CeFe33+(AsO4)(2)(OH)(6), is a new mineral species from Hourt, Stavelot Massif, Belgium. It occurs in the most altered parts of a Devillian quartzite (Lower to Middle Cambrian ... [more ▼]

Graulichite-(Ce), ideally CeFe33+(AsO4)(2)(OH)(6), is a new mineral species from Hourt, Stavelot Massif, Belgium. It occurs in the most altered parts of a Devillian quartzite (Lower to Middle Cambrian), in close association with arsenopyrite, scorodite, mimetite, pharmacosiderite, and goethite. Graulichite-(Ce) forms 80 to 150 mum spherical aggregates of rhombohedral crystals, 50 to 80 mum length, which show the forms {10 (1) over bar2} and {10 (11) over bar}. The mineral is transparent and exhibits a light-green to brownish colour, with a resinous lustre. It is non-fluorescent and shows an irregular fracture, without any perceptible cleavage. The calculated density is 4.42 g/cm(3). Graulichite-(Ce) is uniaxial negative, with a mean refractive index close to 1.97(1) (lambda=590 nm), pleochroic from light green to yellowish. Electron microprobe analyses gave As2O5 31.20, P2O5 0.03, SO3 0.06, SiO2 0.03, Al2O3 3.09, Fe2O3 30.65, SrO 0.24, PbO 0.07, BaO 3.95, CaO 0.03, La2O3 2.26, Ce2O3 15.73, Nd2O3 2.08, H2O (calc.) 8.37, total 97.79 wt. %. The resulting empirical formula, calculated on the basis of 6 cations, is (Ce0.67Ba0.18La0.10Nd0.09Sr0.02)(Sigma1.06) (Fe2.683+Al0.42)(Sigma3.10)[(As(1.89)S(.001)square(0.10))(Sigma2.00)O-8][(OH)(5.57)(H2O)(0.43)](Sigma6.00). The single-crystal unit-cell parameters are a=7.288(2) and c=16.812(9) Angstrom, space group R (3) over barm. The seven strongest lines in the X-ray powder-diffraction pattern [d(in Angstrom)(I)(hkil)] are: 3.052(100)(11 (2) over bar3), 3.636(40)(11 (2) over bar0), 2.239(35)(10 (1) over bar7), 1.817(35)(22 (4) over bar0), 2.792(30)(0006), 5.906(25)(10 (1) over bar1), 1.968(25)(30 (3) over bar3). Graulichite-(Ce) is the iron analogue of arsenoflorencite-(Ce), and belongs to the crandallite mineral group, with the alunite-type structure. The crystal structure of graulichite-(Ce) has been refined, based on single-crystal X-ray diffraction data, to R=0.048. [less ▲]

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See detailMossbauer spectral evidence for next-nearest neighbor interactions within the alluaudite structure of Na1-xLixMnFe2(PO4)(3)
Hermann, Raphaël ULg; Hatert, Frédéric ULg; Fransolet, André-Mathieu ULg et al

in Solid State Sciences (2002), 4(4), 507-513

The Mossbauer spectra of the Na1-xLixMnFe2(PO4)(3) compounds, with x = 0,00, 0.25, 0.50, and 0.75, have been measured between 90 and 295 K and analyzed in terms of a model which takes into account the ... [more ▼]

The Mossbauer spectra of the Na1-xLixMnFe2(PO4)(3) compounds, with x = 0,00, 0.25, 0.50, and 0.75, have been measured between 90 and 295 K and analyzed in terms of a model which takes into account the next-nearest neighbor interactions within the alluaudite structure. Surprisingly, the spectra reveal an unexpected presence of iron(II) in these compounds; the amount of iron(II) is observed to decrease from 19 to 15 atomic percent of the total iron content with increasing x. The temperature dependence of the Fe2+ and Fe3+ isomer shifts agrees with that expected from a second-order Doppler shift and the resulting iron vibrating masses and Mossbauer lattice temperatures are within the expected range of values for iron cations in an octahedral environment. The temperature dependence of the Fe2+ quadrupole splitting has been fit with the Ingalls' model and the results yield a ground state orbital splitting of ca. 500 cm(-1) for the iron(II) sites. The compositional dependence of the isomer shifts and Fe2+ content can be understood in terms of a decrease in the unit-cell volume with increasing substitution of sodium by lithium, a substitution which does not influence the observed quadrupole splittings. (C) 2002 Editions scientifiques et medicales Elsevier SAS. All rights reserved. [less ▲]

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See detailThe crystal chemistry of lithium in the alluaudite structure: A study of the (Na1-xLix)Cdln(2) (PO4)(3) the solid solution (x=0 to 1)
Hatert, Frédéric ULg; Antenucci, Diano ULg; Fransolet, André-Mathieu ULg et al

in Journal of Solid State Chemistry (2002), 163(1), 194-201

Several compounds of the (Na1-xLix)CdIn2(PO4)(3) solid solution were synthesized by a solid-state reaction in air, and pure alluaudite-like compounds were obtained for x = 0.00, 0.25, and 0.50. X-ray ... [more ▼]

Several compounds of the (Na1-xLix)CdIn2(PO4)(3) solid solution were synthesized by a solid-state reaction in air, and pure alluaudite-like compounds were obtained for x = 0.00, 0.25, and 0.50. X-ray Rietveld refinements indicate the occurrence of Cd2+ in the M(1) site, and of In3+ in the M(2) site of the alluaudite structure. This non-disordered cationic distribution is confirmed by the sharpness of the infrared absorption bands. The distribution of Na+ and Li+ on the A(1) and A(2)' crystallographic sites cannot be accurately assessed by the Rietvled method, probably because the electronic densities involved in the Na+ --> Li+ substitution are very small. A comparison with the synthetic alluaudite-like compounds, (Na1-xLix)MnFe2(PO4)(3), indicates the influence of the cations occupying the M(1) and M(2) sites on the coordination polyhedra morphologies of the A(1) and A(2)' crystallographic sites. (C) 2002 Elsevier Science. [less ▲]

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See detailLes minéraux de Belgique
Hatert, Frédéric ULg; Deliens, Michel; Fransolet, André-Mathieu ULg et al

Book - Museum des Sciences Naturelles (2002)

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See detailA Magnetic and Mössbauer Spectral Study of Several Na-Mn-Fe-bearing Alluaudites
Long, Gary J.; Hautot, Dimitri; Hatert, Frédéric ULg et al

Poster (2001)

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See detailFirst experimental evidence of alluaudite-like phosphates with high Li-content: the (Na1-xLix)MnFe2(PO4)3 series (x = 0 to 1).
Hatert, Frédéric ULg; Keller, Paul; Lissner, Falk et al

in European Journal of Mineralogy (2000), 12

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