Naslov
Metavivianite, Fe2+Fe3+2(PO4)2(OH)2·6H2O: new data and formula revision

Autori
Chukanov, N.V. ; Scholz, R. ; Aksenov, S.M. ; Rastsvetaeva, R.K. ; Pekov, I.V. ; Belakovskiy, D.I. ; Krambrock, K. ; Paniago, R.M. ; Righi, A. ; Martins, R.F. ; Belotti, F.M. ; Bermanec, Vladimir

Izvornik
Mineralogical magazine (0026-461X) 76 (2012), 3; 725-741

Vrsta, podvrsta i kategorija rada
Radovi u časopisima, članak, znanstveni

Ključne riječi
metavivianite; formula revision; crystal chemistry; minas gerais; Brazil

Sažetak
The composition, structure, X-ray powder diffraction pattern, optical properties, density, infrared, Raman and Mössbauer spectra, and thermal properties of a homogeneous sample of metavivianite from the Boa Vista pegmatite, near Galiléia, Minas Gerais, Brazil are reported for the first time. Metavivianite is biaxial (+) with α = 1.600(3), β = 1.640(3), γ = 1.685(3) and 2Vmeas = 85(5)°. The measured and calculated densities are Dmeas = 2.56(2) and Dcalc = 2.579 g cm-3. The chemical composition, based on electronmicroprobe analyses, Mössbauer spectroscopy (to determine the Fe2+:Fe3+ ratio) and gas chromatography (to determine H2O) is MgO 0.70, MnO 0.92, FeO 17.98, Fe2O3 26.60, P2O5 28.62, H2O 26.5 ; total 101.32 wt.%. The empirical formula is (Fe3+1.64Fe2+1.23Mg0.085Mn0.06)Σ3.015(PO4)1.98(OH)1.72·6.36H2O. Metavivianite is triclinic, P1, a = 7.989(1), b = 9.321(2), c = 4.629(1) Å, α = 97.34(1), β = 95.96(1), γ = 108.59(2)°, V = 320.18(11) Å3 and Z = 1. The crystal structure was solved using a single-crystal techniques to an agreement index R = 6.0%. The dominant cations in the independent sites are Fe2+ and Fe3+, with multiplicities of 1 and 2, respectively. The simplified crystal-chemical formula for metavivianite is Fe2+ (Fe3+, Fe2+)2(PO4)2(OH, H2O)2·6H2O ; the endmember formula is Fe2+Fe3+2(PO4)2(OH)2·6H2O, which is dimorphous with ferrostrunzite.

Izvorni jezik
Engleski

Znanstvena područja
Geologija

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