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

Author(s)

Inna Lykova, Igor V Pekov, N V Chukanov, Dmitry I. Belakovskiy, Vasiliy O. Yapaskurt, Natalia V Zubkova, Sergey N. Britvin, Gerald Giester

Abstract

The new mineral calciomurmanite, (Na,)

₂Ca(Ti,Mg,Nb)

₄[Si

₂O

₇]

₂O

₂(OH,O)

₂(H

₂O)

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, H

₂O by the Alimarin method) is: Na

₂O 5.39, K

₂O 0.30, CaO 7.61, MgO 2.54, MnO 2.65, FeO 1.93, Al

₂ O

₃ 0.85, SiO

₂ 30.27, TiO

₂ 29.69, Nb

₂O

₅ 6.14, P

₂O

₅ 0.27, H

₂O 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)σ

₄O

_16.40(OH)

_1.60(PO

₄)

_0.03(H

₂O)

_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) Å

³ 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 NaO

₆ and TiO

₆ octahedra and two heteropolyhedral (H) sheets consisting of Si

₂ O

₇ groups, TiO

₆ octahedra and CaO

₈ polyhedra. H

₂O molecules occupy two sites in the interlayer space.

Organisation(s)

Department of Mineralogy and Crystallography

External organisation(s)

Saint Petersburg State University, Russian Academy of Sciences, Fersman Mineralogical Museum, Moscow, Anuchin Research Institute and Museum of Anthropology

Journal

European Journal of Mineralogy: an international journal of mineralogy, geochemistry and related sciences

Volume

28

Pages

835-845

No. of pages

11

ISSN

0935-1221

DOI

https://doi.org/10.1127/ejm/2016/0028-2550

Publication date

06-2016

Peer reviewed

Yes

Austrian Fields of Science 2012

105116 Mineralogy, 105113 Crystallography

Keywords

ASJC Scopus subject areas

Geochemistry and Petrology

Portal url

https://ucrisportal.univie.ac.at/en/publications/c417663e-2ea2-4dab-b1aa-4ec98427b1b7