IMA 2014-100 = arsenowagnerite

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Marco E. Ciriotti
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IMA 2014-100 = arsenowagnerite

Messaggio da Marco E. Ciriotti » sab 21 ott, 2017 13:02

Prossima pubblicazione.

▪ Pekov, I.V., Zubkova, N.V., Agakhanov, A.A., Yapaskurt, V.O., Chukanov, N.V., Belakovskiy, D.I., Sidorov, E.G., Pushcharovsky, D.Yu. (2017): New arsenate minerals from the Arsenatnaya fumarole, Tolbachik volcano, Kamchatka, Russia. VIII. Arsenowagnerite, Mg2(AsO4)F. Mineralogical Magazine, 81, (in press).

A new mineral arsenowagnerite Mg2(AsO4)F, the arsenate analogue of wagnerite, was found in sublimates of the Arsenatnaya fumarole at the Second scoria cone of the Northern reakthrough 21 of the Great Tolbachik Fissure Eruption, Tolbachik volcano, Kamchatka, Russia. It is closely associated with johillerite, tilasite, anhydrite, hematite, fluorophlogopite, cassiterite, calciojohillerite, aphthitalite, and fluoborite. Arsenowagnerite occurs as equant to tabular crystals up to 1 mm across combined in interrupted crusts up to 0.1 x 1.5 x 3 cm. The mineral is transparent, light yellow, lemon-yellow, greenish-yellow or colourless and has a vitreous lustre. Arsenowagnerite is brittle, with Mohs’ hardness of ca 5. Cleavage is distinct, the fracture is uneven. Dcalc = 3.70 g cm–3. Arsenowagnerite is optically biaxial (+), α = 1.614(2), β = 1.615(2), γ = 1.640(2) and 2Vmeas = 25(5)º. Wavenumbers of the strongest absorption bands in the IR spectrum of arsenowagnerite (cm–1) are: 874, 861, 507, 491, and 470. The chemical composition (average of 6 electron-microprobe analyses, wt.%) is: MgO 38.72, CaO 0.23, MnO 0.32, CuO 31 0.60, ZnO 0.05, Fe2O3 0.11, TiO2 0.03, SiO2 0.08, P2O5 0.18, V2O5 0.03, As2O5 54.96, SO3 0.10, F 8.91, –O=F –3.75, total 100.57. The empirical formula calculated on the basis of 5 (O+F) apfu is: Mg1.98Cu0.02Mn0.01Ca0.01)Σ2.02(As0.99P0.01)Σ1.00O4.03F0.97. Arsenowagnerite is monoclinic, P21/c, (34) a = 9.8638(3), b = 12.9830(3), c = 12.3284(3) Å, β = 109.291(3)°, V = 1490.15(7) Å3 and Z = 16. The strongest reflections of the powder X-ray diffraction pattern [d,Å(I)(hkl)] are: 5.80(41)(002), 5.31(35)(120), 3.916(37)(-221), 3.339(98)(221, 023), 3.155(65)(202), 3.043(100)(-141), 2.940(72)(-204), 2.879(34)(-322), and 2.787(51)(320, -124). The crystal structure was solved from single-crystal X-ray diffraction data, R = 0.0485. Arsenowagnerite is isostructural to wagnerite-Ma2bc. The crystal structure is built by almost regular AsO4 tetrahedra, distorted MgO4F2 octahedra and distorted MgO4F trigonal bipyramids.
Marco E. Ciriotti

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