Vasilseverginite, Cu9O4(AsO4)(2)(SO4)(2), a new fumarolic mineral with a hybrid structure containing novel anion-centered tetrahedral structural units

摘要

The new mineral vasilseverginite, ideally Cu9O4(AsO4)(2)(SO4)(2), 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 tenorite, lammerite, stranskiite, lammerite-beta, langbeinite, dolerophanite, sanidine, hematite, and gahnite. Vasilseverginite occurs as prismatic crystals up to 0.02 x 0.02 x 0.06 mm(3) combined in groups or interrupted crusts up to 1 x 2 cm(2) in area and up to 0.1 nun thick. It is transparent, bright green, with vitreous luster. D-calc is 4.41 g.cm(-3). Vasilseverginite is optically biaxial (-), alpha 1.816(5), beta 1.870(5), gamma 1.897(5), estimated 2V is 30(15)degrees. Chemical composition (wt%, electron-microprobe) is: CuO 64.03, ZnO 0.79, Fe2O3 0.25, P2O5 0.05, As2O5 20.83, SO 3 14.92, total 100.87. The empirical formula calculated on O = 20 apfu is (Cu8.78Zn0.11Fe0.033+)(Sigma 8).92As1.98P0.01S2.03O20. Vasilseverginite is monoclinic, P2(1)/n, a = 8.1131(4), b = 9.9182(4), c = 11.0225(5) angstrom, beta = 110.855(2)degrees, V = 828.84(6) angstrom(3), and Z = 2. The strongest reflections in the powder XRD pattern [d,angstrom(I)(hkl)] are: 7.13(41)(10 (1) over bar), 5.99(70)(110, 11 (1) over bar), 5.260(100)(101), 4.642(46)(111), 3.140(31)(03 (1) over bar), 2.821(35)(02 (3) over bar), 2.784(38)(13 (2) over bar, 03 (2) over bar), 2.597(35)(20 (4) over bar), and 2.556(50) (23 (1) over bar, 212). The crystal structure, solved using single-crystal X-ray diffraction data, R-1 = 0.025, is based upon complex [O4Cu9](10+) layers parallel to ((1) over bar 01) that are composed of edge- and corner-sharing (OCu4) tetrahedra. The topology is unprecedented in inorganic structural chemistry. The crystal structure can be considered a hybrid of the structures of popovite Cu5O2(AsO4)(2) and dolerophanite Cu2O(SO4) according to the scheme Cu9O4(AsO4)(2)(SO4)(2) = Cu5O2(AsO4)(2) + 2Cu(2)O(SO4). The chemical hybridization does not result in a significant increase in chemical complexity of vasilseverginite compared to the sum of those of popovite and dolerophanite, whereas the structural hybridization leads to the doubling of structural information per unit cell. The mineral is named in memory of the outstanding Russian mineralogist, geologist, and chemist Vasiliy Mikhailovich Severgin (1765-1826).