Alteration sequences of aluminium phosphates from Montebras pegmatite, Massif Central, France

Poster (2007)

New structural data on synthetic alluaudite-type phosphates

Poster (2007)

The wyllieite group of minerals : crystal chemistry, nomenclature and stability

Conference (2006)

The stability of iron-rich alluaudites in granitic pegmatites : an experimental investigation of the Na-Fe(II)-Fe(III) (+PO4) system

in Berichte der Deutschen Mineralogischen Gesellschaft : Beihefte zum European Journal of Mineralogy (2006), 18

Occurrence of sursassite, Mn2Al3(SiO4)(Si2O7)(OH)3, in the Lienne Valley, Stavelot Massif

Conference (2006)

Hydrothermal synthesis and crystal structure of Na(Na,Mn)(7)Mn-22(PO4)(18)0.5H(2)O, a new compound of fillowite structure type

in European Journal of Mineralogy (2006), 18(6), 765-774

The chemical compound Na(Na,Mn)(7)Mn-22(PO4)(18)center dot 0.5H(2)O was synthesized with a Tuttle pressure vessel at 800 degrees C and 1 kbar during experimental investigations on the conditions of ... [more ▼]

The chemical compound Na(Na,Mn)(7)Mn-22(PO4)(18)center dot 0.5H(2)O was synthesized with a Tuttle pressure vessel at 800 degrees C and 1 kbar during experimental investigations on the conditions of fillowite formation. The crystal structure of a single-crystal, space group R (No. 148), a = 15.2741(9), c = 43.334(3) angstrom, Z = 6, was determined from X-ray intensity data and refined up to R-1 = 0.0728 and R-l{FO > 4 sigma(FO)} = 0.0546. The crystal structure of Na(Na,Mn)(7)Mn-22(PO4)(18)center dot 0.5H(2)O is similar to the structure of fillowite, Na6Ca3(Mn,Fe)(21)(PO4)(18.), but a significant difference between the synthetic H2O containing compound and fillowite is the replacement of (Na12)O-8(-) by Mn(H2O)(2)O-5(-) polyhedra, which form characteristic six-member rings. The coordination polyhedra around Na12 and Mn12 are so different that simple isomorphous substitution of Na12 by Mn12 is very unlikely, but whole six-member rings either of (Na12)O-8(-) or (Mn12)(H2O)(2)O-5 polyhedra seem to be distributed statistically over the crystal structure. No indication for ordering, e.g. sheet by sheet, has been observed. Na(Na,Mn)(7)Mn-22(PO4)(18)center dot 0.5H(2)O is the first fillowite-like compound for which water is located in the structure from single-crystal study. This result is proved by infrared spectral data and indicates that water can play an essential role in the fillowite structure-type. Structural features of the synthetic compounds Na(Na,Mn)(7)Mn-22(PO4)(18)center dot 0.5H(2)O, Na4Ca4Mg21(PO4)(18) and fillowite are compared. [less ▲]

Crystal chemistry of the hydrothermally synthesized Na-2(Mn1-xFex2+)(2)Fe3+(PO4)(3) alluaudite-type solid solution

in American Mineralogist (2005), 90(4), 653-662

Several compounds of the Na-2(Mn1-xFex2x)(2)Fe3+(PO4)(3) solid solition have been hydrothermally synthesized at 400 degrees C and 1 kbar; pure alluaudite-like compounds have been obtained for x = 0.00, 0 ... [more ▼]

Several compounds of the Na-2(Mn1-xFex2x)(2)Fe3+(PO4)(3) solid solition have been hydrothermally synthesized at 400 degrees C and 1 kbar; pure alluaudite-like compounds have been obtained for x = 0.00, 0.25, 0.50, 0.75, and 1.00. Rietveld refinements of the powder X-ray diffraction patterns indicate the presence of Na+ at the Al and A2' sites, Mn2+ and Fe2+ at the M1 site, and Mn2+, Fe2+, and Fe3+ at the M2 site. The presence of small amounts of Na+ at the M1 site and Mn2+ at the Al site indicates a partially disordered distribution of these cations. An excellent linear correlation has been established between the M1-M2 distance and the energy of the infrared band attributed to the M2+-O vibrations. The Mossbauer spectra, measured between 85 and 295 K, were analyzed in terms of a model which includes the next-nearest neighbor interactions at the M2 and M1 crystallographic sites. Fe2+ and Fe3+ isomer shifts are typical of the alluaudite structure and exhibit the expected second-order Doppler shift. The derived iron vibrating masses and Mossbauer lattice temperatures are within the range of values expected for iron cations in all octahedral environment. The Fe2+ and Fe3+ quadrupole splittings are typical of the alluaudite structure, and the temperature dependence of the Fe2+ quadrupole splitting was fit with the Ingalls model, which yielded a ground state orbital splitting of ca. 460 to 735 cm(-1) for the Fe2+ sites. The isomer shifts and quadrupole splittings of Fe2+ at the M1 site are larger than those of Fe2+ at M2, indicating that the M1 site is both larger and more distorted than the M2 site. [less ▲]

Stability of the alluaudite + triphylite paragenesis in granitic pegmatites, and first experimental evidence of sodium incorporation into triphylite

Conference (2005)

A structural, magnetic, and Mossbauer spectral study of several Na-Mn-Fe-bearing alluaudites

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 ▲]

Natural and synthetic alluaudite-type phosphates : crystal chemistry and applications

Conference (2004)