New arsenate minerals from the Arsenatnaya fumarole, Tolbachik volcano, Kamchatka, Russia. XIII. Pansnerite, K3Na2Fe63+(AsO4)(8)

摘要

The new mineral pansnerite, ideally K3Na2Fe63+(AsO4)(8), was found in the Arsenatnaya fumarole at the Second scoria cone of the Northern Breakthrough of the Great Tolbachik Fissure Eruption, Tolbachik volcano, Kamchatka, Russia. It is associated with aphthitalite, hematite, sanidine, badalovite, khrenovite, achyrophanite, arsenatrotitanite, ozerovaite, tilasite, calciojohillerite, johillerite, nickenichite, svabite, katiarsite, yurmarinite, anhydrite, rutile, cassiterite and pseudobrookite. Pansnerite forms tabular to lamellar (flattened on {010}), usually pseudohexagonal crystals up to 0.2 mm x 0.7 mm x 1 mm and crystal clusters up to 2 mm across. It is transparent to translucent, light green, pale greenish, yellowish-greenish or yellowish, with vitreous lustre. The mineral is brittle, with perfect {010} cleavage. The Mohs' hardness is ca 3. D-calc is 3.596 g cm(-3). Pansnerite is optically biaxial (-), alpha = 1.702(4), beta = 1.713(4), gamma = 1.717(4), 2V(meas) = 45(10)degrees and 2V(calc) = 62 degrees. Chemical composition (holotype, wt.%, electron microprobe data) is: Na(2)O6.39, K2O 8.52, CaO 0.08, MgO 0.08, MnO 0.02, NiO 0.02, CuO 1.35, ZnO 0.34, Al2O3 7.35, Cr2O3 0.04, Fe2O3 16.72, SiO2 0.16, P2O5 0.22, V2O5 0.09, As2O5 57.76, SO3 0.04, total 99.20. The empirical formula based on 32 O apfu is K2.86Na3.26Ca0.02(Fe3.313+Al2.28Cu0.27Zn0.07Mg0.03Cr0.01)(Sigma 5.97)(As7.95P0.05Si0.04V0.02S0.01)(Sigma 8.06)O-32. Pansnerite is orthorhombic, Cmce, a = 10.7372(3), b= 20.8367(8), c = 6.47335(15) angstrom, V= 144827(7) angstrom(3) and Z= 2. The strongest reflections of the X-ray powder diffraction pattern [d,angstrom(I)(hkl)] are: 10.49(100)(020), 5.380(88)(111), 4.793(65)(220), 3.105(46)(311, 002), 3.079(32) (112, 061), 2.932(35)(260), 2.783(65)(202) and 2.694(52)(400, 222). The crystal structure was solved from single-crystal X-ray diffraction data, R-1 = 2.82%. The structure is based on heteropolyhedral layers formed by MO6 octahedra (M= Fe3+ and Al) sharing common vertices and connected by AsO4 tetrahedra. Na+ and K+ cations are located in the intertayer space. The mineral is named in honour of the GermanRussian mineralogist and geographer Lavrentiy Ivanovich Pansner (1777-1851). Pansnerite forms a solid-solution series with the isotypic mineral ozerovaite, ideally KNa2Al3(AsO4)(4).