Crystal structure of a Na,K-variety of merlinoite

The crystal structure of the mineral merlinoite Na5K7(H2O)(24)[Al12Si20O64] was established by the method of X-ray diffraction analysis. X-ray data we re collected on a STOE IPDS diffractometer (lambda MoKalpha radiation, grap hite monochromator, T= 120 K, 2 theta(max) = 62 degrees, R = 0.0434 based o n 1471 reflections) from a twinned crystal [the (110) twinning parameter is 0.245]: a = 13.863(3) Angstrom, b = 14.135(2) Angstrom, c = 10.047(2) Angs trom, sp. gr. D-2h(25) = Immm, Z = 1, p(calcd) = 2.269 g/cm(3). Unlike mine rals studied earlier, merlinoite, a new rare variety of zeolite, does not c ontain alkaline-earth cations and is characterized by the maximum number of atoms occupying interstices of the tetrahedral Si,Al,O-framework. A compar ative crystallochemical analysis of merlinoites of different compositions h as been performed.