Refinement of the crystal structure of berezanskite, Ti2□2KLi3(Si12O30)

Berezanskite, ideally Ti-2 square 2KLi3(Si12O30), is hexagonal, space group P6/mcc, a = 9.898(4), c = 14.276(6) angstrom, V = 1211.2(9) angstrom(3), Z = 2. The crystal structure was refined to an R-1 index of 2.08% based on 392 unique observed reflections. Berezanskite is isostructural with milarite, ideally (A)Ca(2)(B)o(C)K(T(2))(Be2Al)((Si12O30)-Si-T(1))(H2O)(0-2). The structural unit is of the form[T(2)(3)T(1)(12)O-30] with T(1) = Si and T(2) = Li, inwhich (LiO4) tetrahedra link [Si12O30] six-membered double-rings into a framework. The A, B and C sites occur in the interstices of the framework with the following site populations: A = Ti-2(4+), <A-O> = 1.938(2) angstrom; B = square(2); C = K,<C-O> = 3.058(2) angstrom. In the T(2) = Li-3 milarite-group minerals, the <C-O> distance is inversely related to the occupancy of the B site.