Itelmenite, Na2CuMg2(SO4)(4), a new anhydrous sulfate mineral from the Tolbachik volcano

摘要

Itelmenite, ideally Na2CuMg2(SO4)(4), was found in a fumarole of the Naboko scoria cone of the Tolbachik volcano Fissure Eruption (2012-2013), Kamchatka Peninsula, Russia. Itelmenite occurs as irregularly shaped grains as well as microcrystalline masses associated with anhydrite, saranchinaite, hennarmjahnite, euchlorine, thenardite, aphthitalite and hematite. Itelmenite is orthorhombic, Pbca, a = 9.568(2) angstrom, b= 8.790(2) angstrom, c= 28.715(8) angstrom, V= 2415.0(11) angstrom(3) and Z = 4 (from single-crystal diffraction data). The nine strongest lines of the powder X-ray diffraction pattern are [d(I)(hkl)]: 7.9614(41)(102), 7.1803(32) (004), 5.9122(64)(112), 3.8455(87)(122), 3.6292(52)(214), 3.3931(62)(215), 3.0003(44)(027), 2.9388 (100)(312) and 2.4975(56)(230). The chemical composition determined by the electron-microprobe analysis is (wt.%): Na2O 10.77, K2O 0.20, MgO 11.10, CuO 15.38, ZnO 5.61, SO3 56.42, total 99.48. The empirical formula based on O = 32 apfu is (Na3.93K0.05 )(Sigma 3.98)Mg-3.12(Cu2.19Zn0.78)(Sigma 2.97)S7.97O32. The simplified formula is Na2CuMg2(SO4)(4) taking into account structural data. The crystal structure was solved by direct methods and refined to an agreement index R-1= 0.034 on the basis of 1855 independent observed reflections. The structure of itelmenite is based on a unique type of [A(3)(2+)(SO4)(4)](2) (A = Mg, Cu and Zn) heteropolyhedral framework with voids filled by Na(+)cations.