New Data on the Isomorphism in Eudialyte-Group Minerals. VI: Crystal Structure of the First Member Containing Sulfide Anion with Isomorphic Substitution Cl––S2–

Abstract

An eudialyte-group representative containing S2– sulfide anion has been investigated by X-ray diffraction analysis, electron-probe microanalysis, and IR spectroscopy. The unit-cell parameters are found to be a = 14.2156(3) A, c = 30.405(1) A, and V = 5321.16(3) A3; sp. gr. R3m. The crystal structure is refined to the final reliability factor R = 3.9% in the anisotropic approximation of atomic displacements using 2158 reflections with F > 3σ(F). The idealized formula of the mineral (Z = 3) is [(Na,Н3О)14Sr]Ca6(Mn2Na)Zr3[Si26O72](OH)3S2– · 2H2O. The problems of mineral origin and presence of sulfide sulfur in the minerals with eudialyte-type structure are discussed.