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

Chukanov, Nikita V.; Cipriano, Ricardo Augusto Scholz; Aksenov, Sergey M.; Rastsvetaeva, Ramiza K.; Pekov, Igor V.; Belakovskiy, Dmitriy I.; Krambrock, Klaus Wilhelm Heinrich; Paniago, Roberto Magalhães; Righi, Ariete; Martins, R. F.; Belotti, Ricardo Augusto; Bermanec, Vladimir

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

Date

2012

Authors

Chukanov, Nikita V.

Cipriano, Ricardo Augusto Scholz

Aksenov, Sergey M.

Rastsvetaeva, Ramiza K.

Pekov, Igor V.

Belakovskiy, Dmitriy I.

Krambrock, Klaus Wilhelm Heinrich

Paniago, Roberto Magalhães

Righi, Ariete

Martins, R. F.

Abstract

The composition, structure, X-ray powder diffraction pattern, optical properties, density, infrared, Raman and Mo¨ssbauer spectra, and thermal properties of a homogeneous sample of metavivianite from the Boa Vista pegmatite, near Galile´ia, Minas Gerais, Brazil are reported for the first time. Metavivianite is biaxial (+) with a = 1.600(3), b = 1.640(3), g = 1.685(3) and 2Vmeas = 85(5)º. The measured and calculated densities are Dmeas = 2.56(2) and Dcalc = 2.579 g cm 3. The chemical composition, based on electronmicroprobe analyses, Mo¨ssbauer 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)S3.015(PO4)1.98(OH)1.72·6.36H2O. Metavivianite is triclinic, P1¯ , a = 7.989(1), b = 9.321(2), c = 4.629(1) A ˚ , a = 97.34(1), b = 95.96(1), g = 108.59(2)º, V = 320.18(11) A ˚ 3 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.

Keywords

Metavivianite, Formula revision, Minas Gerais, Crystal chemistry

Citation

CHUKANOV, N. V. et al. Metavivianite, Fe2+Fe3+2(PO4)2(OH)2 6H2O: new data and formula revision. Mineralogical Magazine, v. 76, p. 725-741, 2012. Disponível em: <https://www.degruyter.com/view/j/minmag.2012.76.issue-3/minmag.2012.076.3.20/minmag.2012.076.3.20.xml>. Acesso em: 20 de jun. 2017.