Crystal structures of two ancylite modifications

Abstract

The crystal structures of two ancylite specimens from Khibiny massif (the Kola Peninsula, Russia)—ancylite-(Ce) from alkali hydrothermalites (Sr1.01Ca0.02Ba0.01)Σ1.04(Ce0.52La0.28Nd0.11Pr0.04 Sm0.01)Σ0.96(CO3)2(OH0.83F0.13)Σ0.96 · 0.9H2O and ancylite-(Ce) from carbonatites—have (Sr0.80Ca0.05Ba0.01)Σ0.86(Ce0.62La0.40Nd0.09Pr0.03) Σ1.14(CO3)2(OH0.99F0.15)Σ1.14 · 1.0H2O been refined by the Rietveld method. A focusing STOE-STADIP diffractometer with a bent Ge(111) primary monochromator was used (λ MoK α 1 radiation, 2.16° < 2θ < 54.98°; reflection number 237–437). All the computations for ancylite from alkali hydrothermalites were performed within the sp. gr. Pmc21, a = 5.0634(1) A, b = 8.5898(1) A, c = 7.2781(1) A, V = 316.55(1) A3, R wp = 1.90; the computations for ancylite from carbonatites were performed within the sp. gr. Pmcn, a = 5.0577(1) A, b = 8.5665(2) A, c = 7.3151(2) A, V = 316.94(1) A3, R wp = 2.38 in the anisotropic approximation of thermal vibrations of cations and oxygen atoms.