Structure of lanthanum-rich fluorbritholite-(Ce) from Eifel ...

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Structure of lanthanum-rich fluorbritholite-(Ce) from Eifel - Cation ordering in britholites

Zubkova, N.V., Chukanov, N.V., Pekov, I.V., Schäfer, C., Yapaskurt, V.O., Pushcharovsky, D.Yu. - Lanthanum-Rich Fluorbritholite-(Ce) from Young Alkaline Volcanic Rock of Eifel (Germany) and Its Crystal Structure. Cation Ordering in Britholites. Doklady Earth Sciences, 464 (2015), 936-939

Structure (R=0.0213) of lanthanum-rich fluorbritholite (Ce) [(Ce2.47La2.31Nd0.22Pr0.13Y0.07)5.20Ca4.20Th0.27Mn0.19Sr0.09]9.95(Si5.37P0.63)6O24.16F1.95 from sanidinite in Laacher See, Eifel, Germany was studied on a monocrystal. The structure [space group P63/m, a = 9.58949(13), c = 7.0289(11), V = 559.770(14)] is identical to structures of members of apatite supergroup. Relationships of major cations in polyhedra M(1)O9 = (Ca0.6REE0.4), and in polyhedral M(2)O6F = (REE0.7Ca0.3). Substantial structural order M(1) and M(2) is defined, simplified structural formula: (Ca, LREE)2(LREE,Ca)3(SiO4)3F. Analysis of data on crystal chemistry of britholite was carried out. It was demonstrated that distribution of cations on M(1)- and M(2)-positions is always characteristic of partial structural order. Clear tendency of LREE concentration in M(2) position was noted.