IMA 2014-062 = ziminaite

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Marco E. Ciriotti
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IMA 2014-062 = ziminaite

Messaggio da Marco E. Ciriotti » lun 04 dic, 2017 9:19

Prossima pubblicazione.

Referenza:
▪ Pekov, I.V., Siidra, O.I., Yapaskurt, V.O., Polekhovsky, Yu.S., Kartashov, P.M. (2018): Ziminaite, Fe3+VO4, a new howardevansite-group mineral from the Bezymyannyi volcano, Kamchatka, Russia. Mineralogy and Petrology, 112, (in press).

Abstract:
The new mineral ziminaite, ideally Fe3+VO4, was found in fumarole sublimates at the Bezymyannyi volcano, Kamchatka, Russia. Ziminaite occurs as lamellar, tabular or flattened prismatic crystals up to 10 × 30 × 50 μm typically epitaxially overgrowing koksharovite, and as aggregates (up to 0.15 mm) associated with bannermanite in cavities in volcanic scoria. The mineral is translucent, yellowish-brown with an adamantine luster. The calculated density is 3.45 g cm− 3. In reflected light, ziminaite is light grey. Bireflectance is weak, internal reflections are deep yellow. The reflectance values [Rmax–Rmin, % (λ, nm)] are: 17.7–16.3 (470), 15.7–14.1 (546), 15.1–13.8 (589), 14.7–13.6 (650). Chemical composition (wt%) is: MgO 2.20, CaO 0.01, Al2O3 7.81, Fe2O3 27.18, TiO2 4.50, SiO2 0.26, P2O5 0.09, V2O5 57.01, total 99.06. The empirical formula, based on 24 O atoms, is: (Fe3+ 3.29Al1.48Ti0.54Mg0.53)Σ5.84(V6.05Si0.04P0.01)Σ6.10O24 (Z = 1). Ziminaite is triclinic, P-1, a 8.012(4), b 9.345(5), c 6.678(3) Å, α 106.992(10), β 101.547(8), γ 96.594(11)º, V 460.4(4) Å3, Z = 6. The strongest reflections of the powder X-ray diffraction pattern [d,Å(I)(hkl)] are: 3.751(17)(1–21, 12 − 1), 3.539(86)(120), 3.270(67)(01–2), 3.209(100)(2–20), 3.090(20)(2–11, 002), 3.041(18)(03 − 1, 02–2), 2.934(14)(12 − 2, 030) and 1.665(24)(023, 12 − 4). The crystal structure, solved from single-crystal data (R1 = 0.085), is based upon heteropolyhedral framework built by VO4 tetrahedra and Fe3+-centred octahedra and five-fold polyhedra. Ziminaite belongs to the howardevansite group being its first member without species-defining uni- or divalent cations and with all large cation sites vacant. The mineral is named after the Zimina volcano situated near the discovery locality.

NdR: La formula è probabilmente meglio espressa con □Fe3+2Fe3+4(VO4)6.

Howardevansite group
Grigorievite Cu3Fe3+2Al2(VO4)6
Howardevansite Na2Cu2Fe3+4(VO4)6
Koksharovite CaMg2Fe3+4(VO4)6
Ziminaite □Fe3+2Fe3+4(VO4)6
Marco E. Ciriotti

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