The crystal structures of lomonosovite, ideally Na10Ti4(Si2O7)2(PO4)2 O4, a = 5.4170(7) Å, b = 7.1190(9) Å, c = 14.487(2) Å, a = 99.957(3)°, β = 96.711(3)°, γ = 90.360(3)°, V= 546.28(4) Å3, Dcalc. = 3.175 g cm“3, and murmanite, ideally Na4Ti4(Si2O7)2O4(H2O)4, a = 5.3875(6) Å, b = 7.0579(7) Å, c = 12.176(1) Å, a = 93.511(2)°, 0 = 107.943(4)°, y = 90.093(2)°, V = 439.55(2) Å3, Dcalc. = 2.956 g.cm∼3, from the Lovozero alkaline massif, Kola Peninsula, Russia, have been refined in the space group P1̄ (Z = 1) to R values of 2.64 and 4.47%, respectively, using 4572 and 2222 observed |F°≥ 4σF| reflections collected with a single-crystal Bruker AXS SMART APEX diffractometer with a CCD detector and Mo-Kα. radiation. Electron microprobe analysis gave empirical formulae for lomonosovite (Na9.50Mn0.16Ca0.11)Σ9.77(Ti4+2.83Nb0.51Mn0.272+Zr0.11Mg0.11Fe2+0.10Fe3+0.06Ta0.01)Σ4.00(Si2.02O7)2(P0.98O4)2(O3.50F0.50)Σ4, 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 Mössbauer 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, t1 and t2, with t1\ ∼5.5 and t2 ∼7 Å and ttA t2 close to 90°. 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 tx. In murmanite and lomonosovite, the invariant part of the TS block is of composition Na4Ti4(Si2O7)2O4. 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[Na3 (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 located and details of the hydrogen bonding are discussed.

The crystal structure of vigrishinite, ideally NaZnTi4(Si2O7)2O3(OH)(H2O)4, a murmanite-group mineral of the seidozerite supergroup from the type locality, Mt. Malyi Punkaruaiv, Lovozero alkaline massif, Kola Peninsula, Russia, was refined in space group C$\bar 1$, a = 10.530(2), b = 13.833(3), c = 11.659(2) Å, α = 94.34(3), β = 98.30(3), γ = 89.80(3)°, V = 1675.5(2.1) Å3 and R1 = 12.52%. Based on electron-microprobe analysis, the empirical formula calculated on 22 (O + F), with two constraints derived from structure refinement, OH + F = 1.96 pfu and H2O = 3.44 pfu, is: (Na0.67Zn0.21Ca0.05□1.07)Σ2 (Zn0.86□1.14)Σ2(Zn0.14□0.36)Σ0.5(Ti2.60Nb0.62Mn0.30${\rm Fe}_{{\rm 0}{\rm. 23}}^{{\rm 2 +}} $Mg0.10Zr0.06Zn0.05Al0.03Ta0.01)Σ4(Si4.02O14) [O2.60(OH)1.21F0.19]Σ4[(H2O)3.44(OH)0.56]Σ4{Zn0.24P0.03K0.03Ba0.02} with Z = 4. It seems unlikely that constituents in the {} belong to vigrishinite itself. The crystal structure of vigrishinite is an array of TS blocks (Titanium Silicate) connected via hydrogen bonds. The TS block consists of HOH sheets (H = heteropolyhedral and O = octahedral) parallel to (001). In the O sheet, the Ti-dominant MO(1,2) sites, Na-dominant MO(3) and □-dominant MO(4) sites give ideally Na□Ti2 pfu. In the H sheet, the Ti-dominant MH(1,2) sites, Zn-dominant AP(1) and vacant AP(2) sites give ideally Zn□Ti2 pfu. The MH and AP(1) polyhedra and Si2O7 groups constitute the H sheet. The ideal structural formula of vigrishinite of the form ${\rm A}_{\rm 2}^{P} {\rm M}_{\rm 2}^{\rm H} {\rm M}_{\rm 4}^{\rm O} $(Si2O7)2(${\rm X}_{\rm M}^{\rm O} $)2(${\rm X}_{\rm A}^{\rm O} $)2(${\rm X}_{{\rm M,A}}^{P} $)4 is Zn□Ti2Na□Ti2(Si2O7)2O2O(OH)(H2O)4. Vigrishinite is a Zn-bearing, Na-poor and OH-rich analogue of murmanite, ideally Na2Ti2Na2Ti2(Si2O7)2O2O2(H2O)4. Murmanite and vigrishinite are related by the following substitution: H(${\rm Na}_{\rm 2}^{\rm +} $)mur + O(Na+)mur + O(O2–)mur ↔ H(Zn2+)vig + H(□)vig + O(□)vig + O[(OH)–]vig. The doubling of the t1 and t2 translations of vigrishinite compared to those of murmanite is due to the order of Zn and □ in the H sheet and Na and □ in the O sheet of vigrishinite.