Modular structure of a potassium-rich analogue of eudialyte with a doubledparameter c

The structure of a new potassium-rich representative of the eudialyte group described by the idealized formula Na27K8Ca12Fe3Zr6[Si52O144](O,OH,H2O)(6) Cl-2 was established by the methods of the X-ray diffraction analysis (R = 0.045, 3900 reflections). The unit-cell parameters are a = 14.249(1) Angstr om, c = 60.969(7) Angstrom, V = 10 720.3 Angstrom (3), sp. gr. R3m. The str ucture of the mineral is characterized by in-layer order in cation arrangem ent resulting in doubling of the parameter c and the formation of two diffe rent modules, of which one corresponds to composition and structure of eudi alyte (with an admixture of kentbrooksite) and the other is the derivative of alluaivite. (C) 2001 MAIK "Nauka/Interperiodica".