The new mineral calciomurmanite, (Na,)₂Ca(Ti,Mg,Nb)₄[Si₂O₇]₂O₂(OH,O)₂(H₂O)₄, a Na-Ca ordered analogue of murmanite, was found in three localities at Kola Peninsula, Russia: at Mt. Flora in the Lovozero alkaline complex (the holotype) and at Mts. Eveslogchorr (the cotype) and Koashva, both in the Khibiny alkaline complex. Calciomurmanite is a hydrothermal mineral formed as a result of late-stage, lowerature alteration (hydration combined with natural cation exchange) of a higherature, anhydrous phosphate-bearing titanosilicate, most likely lomonosovite and/or betalomonosovite, in the peralkaline (hyperagpaitic) rocks. The holotype sample is associated with microcline, aegirine, lorenzenite and fluorapatite, whereas the cotype sample occurs with microcline, aegirine, lamprophyllite, tsepinite-Ca and tsepinite-K. The mineral occurs as lamellae up to 0.1 × 0.4 × 0.6 cm, sometimes combined in fan-shaped aggregates up to 3.5 cm. Calciomurmanite is pale brownish or purple; the streak is white. The lustre is nacreous on cleavage surface and greasy on broken surface across cleavage. The (001) cleavage is perfect, mica-like; the fracture is stepped. D_meas = 2.70(3), D_calc = 2.85 g cm^-3. The mineral is optically biaxial (-), α = 1.680(4), β = 1.728(4), γ = 1.743(4), 2V_meas = 58(5)°. The IR spectrum is reported. The chemical composition (wt%, electron-microprobe data, H₂O by the Alimarin method) is: Na₂O 5.39, K₂O 0.30, CaO 7.61, MgO 2.54, MnO 2.65, FeO 1.93, Al₂ O₃ 0.85, SiO₂ 30.27, TiO₂ 29.69, Nb₂O₅ 6.14, P₂O₅ 0.27, H₂O 11.59, total 99.23. The empirical formula of the holotype sample, calculated on the basis of Si + Al = 4 apfu, is: Na_1.34Ca_1.04K_0.05Mg_0.49Mn_0.29Fe_0.21Nb_0.36Ti_2.85(Si_3.87Al_0.13)σ₄O_16.40(OH)_1.60(PO₄)_0.03(H₂O)_4.94. Calciomurmanite is triclinic, P-1, a = 5.3470(6), b = 7.0774(7), c = 12.146(1) Å, α = 91.827(4), β = 107.527(4), γ = 90.155(4)°, V = 438.03(8) ų and Z = 1. The strongest reflections of the X-ray powder pattern [d,A(I)(hkl)] are: 11.69(100)(001), 5.87(68)(011, 002), 4.25(89) (-1-11, -111), 3.825(44)(-1-12, 003, -112), 2.940(100)(-1-21, -121), 2.900(79)(004, 120). The crystal structure was solved by direct methods from single-crystal lowerature (200 K) X-ray diffraction data and refined to R = 0.0656 for the holotype and 0.0663 for the cotype. The structure is based on a three-sheet HOH block: an octahedral (O) sheet containing alternating chains of NaO₆ and TiO₆ octahedra and two heteropolyhedral (H) sheets consisting of Si₂ O₇ groups, TiO₆ octahedra and CaO₈ polyhedra. H₂O molecules occupy two sites in the interlayer space.