Belousovite, KZn(SO₄)Cl, a new sulfate mineral from the Tolbachik volcano with apophyllite sheet-topology.

Belousovite, ideally KZn(SO₄)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, P2₁/c, a = 6.8904(5), b = 9.6115(7), c = 8.2144(6) Å, β = 96.582(2), V = 540.43(7) ų and Z = 4 (from single-crystal diffraction data). The eight strongest lines of the powder X-ray diffraction pattern are [d_meas Å(I)(hkl)]: 6.8451(100)(100), (3.6401)(71)(⁠|$\bar{1}$|21), (3.1592)(84)(1|$\bar{1}$|2), (3.1218)(41)(⁠|$\bar{2}$|11), (3.1140)(52)(022), (2.9812)(41)(031), (2.9121)(44)(130) and (2.0483)(19)(⁠|$\bar{3}$|12). The chemical composition determined by the electron-microprobe analysis is (wt.%): K₂O 19.55, Rb₂O 0.58, ZnO 34.85, SO₃ 34.65, Cl 14.77, –O = Cl₂ 3.34, total 101.06. The empirical formula based on O + Cl = 5 apfu is K_0.97Rb_0.01Zn_1.00S_1.01O_4.03Cl_0.97. The simplified formula is KZn(SO₄)Cl. The crystal structure was solved by direct methods and refined to R₁ = 0.029 on the basis of 1965 independent observed reflections. The structure of belousovite consists of infinite [ZnSO₄Cl]^– layers and K⁺ ions. [ZnSO₄Cl]^– layers are formed by corner sharing mixed-ligand ZnO₃Cl tetrahedra and SO₄ tetrahedra. The topology of [ZnSO₄Cl]^– layers in belousovite is identical to [Si₄O₁₀]^4– layers in the minerals of the apophyllite group. A review of mixed-ligand ZnO_mCl_n coordination polyhedra in minerals and inorganic compounds is given.