The crystal structures of lomonosovite, ideally Na10Ti4(Si2O7)(2)(PO4)(2) O-4 a = 5.4170(7) angstrom, b = 7.1190(9) angstrom, c = 14.487(2) angstrom, alpha = 99.957(3)degrees, beta = 96.711(3)degrees, gamma = 90.360(3)degrees, V = 546.28(4) angstrom(3), D-calc. = 3.175 g cm(-3), and murmanite, ideally Na4Ti4(Si2O7)(2)O-4(H2O)(4), a = 5.3875(6) angstrom, b = 7.0579(7) angstrom, c = 12.176(1) angstrom, alpha = 93.511(2)degrees, beta = 107.943(4)degrees, gamma = 90.093(2)degrees, V = 439.55(2) angstrom(3), D-calc. = 2.956 g.cm(-3), from the Lovozero alkaline massif, Kola Peninsula, Russia, have been refined in the space group P (1) over bar (Z = 1) to R values of 2.64 and 4.47%, respectively, using 4572 and 2222 observed vertical bar F-o >= 4 sigma F vertical bar reflections collected with a single-crystal Bruker AXS SMART APEX diffractometer with a CCD detector and Mo-K alpha radiation. Electron microprobe analysis gave empirical formulae for lomonosovite (Na9.50Mn0.16Ca0.11)(Sigma 9.77)(Ti2.834+Nb0.51Mn0.272+Zr0.11Mg0.11Fe0.102+Fe0.063+Ta0.01)(Sigma 4.00)(Si2.02O7)(2) (P0.98O4)(2)(O3.50F0.50)(Sigma 4), Z = 1, calculated on the basis of 26(O+F) a.p.f.u., and murmanite (Na3.32Mn0.15Ca0.21K0.05)(Sigma 3.73)(Ti3.084+Nb0.51Mn0.182+Fe0.153+Mg0.07Zr0.01)(Sigma 4.00)(Si1.98O7)(2)(O3.76F0.24)(Sigma 4) (H2O)(4), Z = 1, calculated on the basis of 22 (O+F) a.p.f.u., with H2O determined from structure refinement and Fe3+/(Fe2++Fe3+) ratios obtained by Mossbauer spectroscopy. The crystal structures of lomonosovite and murmanite are a combination of a titanium silicate (TS) block and an intermediate (I) block. The TS block consists of HOH sheets (H-heteropolyhedral, O-octahedral), and is characterized by a planar cell based on translation vectors, t(1) and t(2), t(1) similar to 5.5 and t(2) similar to 7 angstrom and t(1) boolean AND t(2) close to 90 degrees. The TS block exhibits linkage and stereochemistry typical for Group IV (Ti = 4 a.p.f.u.) of the Ti disilicate minerals: two H sheets connect to the O sheet such that two (Si2O7) groups link to Ti polyhedra of the O sheet adjacent along t(1). In murmanite and lomonosovite, the invariant part of TS block is of composition Na4Ti4(Si2O7)(2)O-4. There is no evidence of vacancy-dominant cation sites or (OH) groups in the O sheet of lomonosovite or murmanite. In lomonosovite, the I block is a framework of Na polyhedra and P tetrahedra which gives 2[Na-3 (PO)(4)] p.f.u. In murmanite, there are four (H2O) groups in the intermediate space between TS blocks. In lomonosovite, TS and I blocks alternate along c. In murmanite, TS blocks are connected via hydrogen bonding. The H atoms were locted and details of the hydrogen bonding are discussed.
