TY - JOUR

T1 - Calciomurmanite, (Na,)2Ca(Ti,Mg,Nb)4[Si2O7]2O2(OH,O)2(H2O)4, a new mineral from the Lovozero and Khibiny alkaline complexes, Kola Peninsula, Russia

AU - Lykova, Inna S.

AU - Pekov, Igor V.

AU - Chukanov, Nikita V.

AU - Belakovskiy, Dmitry I.

AU - Yapaskurt, Vasiliy O.

AU - Zubkova, Natalia V.

AU - Britvin, Sergey N.

AU - Giester, Gerald

PY - 2016

Y1 - 2016

N2 - 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. Dmeas = 2.70(3), Dcalc = 2.85 g cm-3. The mineral is optically biaxial (-), α = 1.680(4), β = 1.728(4), γ = 1.743(4), 2Vmeas = 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: Na1.34Ca1.04K0.05Mg0.49Mn0.29Fe0.21Nb0.36Ti2.85(Si3.87Al0.13)σ4O16.40(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) Å3 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.

AB - 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. Dmeas = 2.70(3), Dcalc = 2.85 g cm-3. The mineral is optically biaxial (-), α = 1.680(4), β = 1.728(4), γ = 1.743(4), 2Vmeas = 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: Na1.34Ca1.04K0.05Mg0.49Mn0.29Fe0.21Nb0.36Ti2.85(Si3.87Al0.13)σ4O16.40(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) Å3 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.

KW - Calciomurmanite

KW - Crystal structure

KW - Heterophyllosilicate mineral

KW - Ion exchange

KW - Khibiny alkaline complex

KW - Lovozero alkaline complex

KW - Murmanite

KW - New mineral

KW - Peralkaline rock

KW - Titanosilicate

UR - http://www.scopus.com/inward/record.url?scp=84996602605&partnerID=8YFLogxK

U2 - 10.1127/ejm/2016/0028-2550

DO - 10.1127/ejm/2016/0028-2550

M3 - Article

AN - SCOPUS:84996602605

VL - 28

SP - 835

EP - 845

JO - European Journal of Mineralogy

JF - European Journal of Mineralogy

SN - 0935-1221

IS - 4

ER -