Titre du document / Document title

New minerals tsepinite-K (K, Ba, Na)²(Ti, Nb)² (Si⁴O¹²)(OH, O)².3H²O and paratsepinite-Ba (Ba, Na, K)^2-x(Ti, Nb)²(Si⁴O¹²)(OH, O)².4H²O and their relationship with other labuntsovite group members

Auteur(s) / Author(s)

CHUKANOV N. V. ; PEKOV I. V. ; ZADOV A. E. ; ROSENBERG K. A. ; RASTSVETAEVA R. K. ; KRIVOVICHEV S. V. ; LEVITSKAYA L. A. ;

Résumé / Abstract

New minerals of labintsovite-group: tsepinite-K and paratsepinite-Ba, were discovered in the well known Khibiny-Lovozero alkaline complex (Kola peninsula, Russia). The minerals were named as K- and Ba-bearing analogs, with doubled c parameter, of tsepinite-Na. Tsepinite-K was discovered in alkaline pegmatites at Karnasurt Mt. (Lovozero) as short-prismatic colourless crystals up to 0.4 mm length (main forms {001}, {010}, {100} and {-201}) in pseudomorphs after murmanite, in association with other labuntsovite-group minerals, manganneptunite, aegirine, natrolite, chabasite-Ca, etc. (holotype), and at Eveslogchorr and Kukisvumchorr Mts. (Khibiny). Paratsepinite-Ba was found as imperfect long-prismatic light-brown crystals, up to 5 mm long, together with other labuntsovite-group minerals, titanite, aegirine, eudialyte, larnprophyllite, lorenzenite, natrolite, vinogradovite, tundrite-(Ce), etc. in alkaline pegmatite at Lepkhe-Nelm Mt. (Lovozero). Tsepinite-K and paratsepinite-Ba are brittle; cleavage non-perfect, Mobs' hardness 5, Both are monoclinic, optically biaxial, positive, 2V = 25-40°, a 1.690 (3) and 1.667 (2), β 1.701 (3) and 1.674 (2), y 1.800 (5) and 1.770 (5); D^meas= 2.88 (3) and 2.88 (3) g/cm₃, D^cale = 2.97 and 2.91 g/cm₃ respectively, In crystal structures R = 0.032 and 0.072, respectively. For tsepinite-K space group is Cm, a = 14.327 (3), b = 13.802 (2), c = 7.783 (1) Å, β = 116.95 (1)°, V = 1372 Å₃, Z = 4; for paratsepinite-Ba space group is C2/m, a = 14.551 (2), b = 14.01 (2), c = 15.702 (3) Å, β = 117.58 (1)°, V= 2835 Å₃, Z = 8. The strongest lines of the powder diffraction pattern [d, Å (1, %) (hkl)] are - tsepinite-K: 6.87 (100) (001, 020), 3.20 (60) (400), 3.05 (80) (022, 041), 3.00 (60) (240, 24-1), 2.56 (90) (241, 24-2, 20--3, 331); paratsepinite-Ba: 7.11 (100) (020), 4.08 (80) (310), 3.95 (100) (202, 20-4), 3.24 (90) (400, 40-4), 3.11 (80) (042, 024), 2.403 (80) (60-2). Chemical compositions of the holotype samples of tsepinite-K and paratsepinite-Ba (wt. %, electron probe, H²O content-by thermogravimetrical method): Na²O 2.14 and 1.80; K²O 6.54 and 1.69; CaO - 0 and 0.51; SrO 0 and 1.96; BaO 11.28 and 11.02; MnO 1.15 and 1.25; FeO 0.37 and 0; Al²O³ 0 and 0.22; SiO² 38.86 and 38.86; TiO² 21.47 and 17.73; Nb²O⁵ 7.05 and 11.60; H²O 10.34 and 12.86; total 99.20 and 98.58. Their empirical formulae are, respectively: (K^0.86Ba^0.46Na^0.43Mn^0.10)^Σ1.85(Ti^1.66Nb^0.33Fe^0.033+)^Σ2.02Sι⁴O¹²(OH)^1.21O^0.792.94H²O; (Ba^0.46Na^0.37K^0.23 Mn^0.10Ca^0.06)^Σ1.35(Ti^1.40Nb^0.55)^Σ1.95(Si^3.97Al^0.03O¹²)(OH)^1.58O^0.42.3.7H²O. Simplified formulae are: (K,Ba,Na)² (Ti,Nb)²(Si⁴O¹²)(OH,O)².3H²O and (Ba,Na,K)^2-x(Ti,Nb)²(Si⁴O¹²)(OH,O)².4H²O. Type material of the minerals is deposited in Fersman Mineralogical Museum, Russian Academy of Sciences, Moscow.

Revue / Journal Title

Zapiski Vserossijskogo mineralogičeskogo obŝestva   ISSN 0869-6055 

Source / Source

2003, vol. 132, n^o1, pp. 38-51 [14 page(s) (article)]

Langue / Language

Russe

Editeur / Publisher

Nauka, Sankt-Peterburg, RUSSIE, FEDERATION DE  (1992) (Revue)

Localisation / Location

INIST-CNRS, Cote INIST : 4673, 35400011679348.0040