Belousovite, KZn(SO (sub 4) )Cl; a new sulfate mineral from the Tolbachik Volcano with apophyllite sheet-topology

Belousovite, ideally KZn(SO (sub 4) )Cl, was found in a Yadovitaya fumarole of the Second scoria cone of the North Breach of the Great Tolbachik Fissure Eruption (1975-1976), Tolbachik volcano, Kamchatka Peninsula, Russia. Belousovite occurs as irregularly-shaped grains and in the form of microcrystalline masses associated with kamchatkite, langbeinite, euchlorine, anglesite and zincite. Belousovite is monoclinic, P2 (sub 1) /c, a = 6.8904(5), b = 9.6115(7), c = 8.2144(6) Aa, beta = 96.582(2), V = 540.43(7) Aa (super 3) and Z = 4 (from single-crystal diffraction data). The eight strongest lines of the powder X-ray diffraction pattern are [d (sub meas) Aa(I)(hkl)]: 6.8451(100)(100), (3.6401)(71)(121), (3.1592)(84)(112), (3.1218)(41)(211), (3.1140)(52)(022), (2.9812)(41)(031), (2.9121)(44)(130) and (2.0483)(19)(312). The chemical composition determined by the electron-microprobe analysis is (wt.%): K (sub 2) O 19.55, Rb (sub 2) O 0.58, ZnO 34.85, SO (sub 3) 34.65, Cl 14.77, -O = Cl (sub 2) 3.34, total 101.06. The empirical formula based on O + Cl = 5 apfu is K (sub 0.97) Rb (sub 0.01) Zn (sub 1.00) S (sub 1.01) O (sub 4.03) Cl (sub 0.97) . The simplified formula is KZn(SO (sub 4) )Cl. The crystal structure was solved by direct methods and refined to R (sub 1) = 0.029 on the basis of 1965 independent observed reflections. The structure of belousovite consists of infinite [ZnSO (sub 4) Cl] (super -) layers and K (super +) ions. [ZnSO (sub 4) Cl] (super -) layers are formed by corner sharing mixed-ligand ZnO (sub 3) Cl tetrahedra and SO (sub 4) tetrahedra. The topology of [ZnSO (sub 4) Cl] (super -) layers in belousovite is identical to [Si (sub 4) O (sub 10) ] (super 4-) layers in the minerals of the apophyllite group. A review of mixed-ligand ZnO (sub m) Cl (sub n) coordination polyhedra in minerals and inorganic compounds is given.