Ziminaite, Fe3+VO4, a new howardevansite-group mineral from the Bezymyannyi volcano, Kamchatka, Russia

摘要

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 x 30 x 50 mu m 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 [R (max) -R (min), % (lambda, 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)(I 5.84)(V6.05Si0.04P0.01)(I pound 6.10)O-24 pound (Z = 1). Ziminaite is triclinic, P , a 8.012(4), b 9.345(5), c 6.678(3) , alpha 106.992(10), beta 101.547(8), gamma 96.594(11)A, V 460.4(4) (3), Z = 6. The strongest reflections of the powder X-ray diffraction pattern [d,(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 (R (1) = 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.