• journal_title：Mineralogical Magazine
• Contributor：N. V. Chukanov ; R. Scholz ; S. M. Aksenov ; R. K. Rastsvetaeva ; I. V. Pekov ; D. I. Belakovskiy ; K. Krambrock ; R. M. Paniago ; A. Righi ; R. F. Martins ; F. M. Belotti ; V. Bermanec
• Publisher：Mineralogical Society of Great Britain and Ireland
• Date：2012-
• Format：text/html
• Language：en
• Identifier：10.1180/minmag.2012.076.3.20
• journal_abbrev：Mineralogical Magazine
• issn：0026-461X
• volume：76
• issue：3
• firstpage：725
• section：Letter

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 2V_meas = 85(5)°. The measured and calculated densities are D_meas = 2.56(2) and D_calc = 2.579 g cm⁻³. The chemical composition, based on electron-microprobe 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 (lass="inline-formula" id="inline-formula-2">lass="math mml" alt="Formula" src="725/embed/mml-math-2.gif" /> lass="inline-formula" id="inline-formula-3">lass="math mml" alt="Formula" src="725/embed/mml-math-3.gif" /> Mg_0.085Mn_0.06)_Σ3.015(PO₄)_1.98(OH)_1.72·6.36H₂O. Metavivianite is triclinic, P1İ, 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) ų 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 lass="inline-formula" id="inline-formula-4">lass="math mml" alt="Formula" src="725/embed/mml-math-4.gif" /> (PO₄)₂(OH)₂·6H₂O, which is dimorphous with ferrostrunzite.