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Titre du document / Document title

Labyrinthite (Na, K, Sr)35Ca12Fe3Zr6TiSi51O144(O, OH, H2O)9Cl3, a new mineral with a modular eudialyte-like structure from Khibiny Alkaline Massif, Kola Peninsula, Russia

Auteur(s) / Author(s)

KHOMYAKOV A. P. ; NECHELYUSTOV G. N. ; RASTSVETAEVA R. K. ;

Résumé / Abstract

Labyrinthite was found on the Nyorkpakhk Mt (Khibiny massif), occurring in hyperagpaitic pegmatite as anhedral rounded grains 0.5-1 cm in cross-size. It associates with potassium feldspar, sodalite, alkaline amphibole, aegirine, pectolite, lamprophyllite, lomonosovite, villiaumite, etc. At the surface, grains of the mineral are replaced by aggregates of zirsinalite, lovozerite and thermonatrite; Color bright pink, streak white, transparent, luster vitreous; brittle, with conchoidal fracture. Mohs' hardness 5-6. D(meas.) =2.88(2) g/cm3 (volumetric method) D(calc.) = 2.87 g/cm3 Optically uniaxial, positive, n0 = 1.597(1), ne = 1.601(1). Trigonal, space group R3, a = 14.239(1), c = 60.733(7) Å, V= 10664(3) Å. Z= 3. The strongest lines of the powder diffraction pattern [d, Å (I)(hkl)] are: 2.977(100)(1.3.10), 2.853(88)(048), 4.324(68)(0.2.10), 3.230(44)(0.2.16), 3.550(39)(220), 2.685(38)(140), 3.049(36)(1.1.18), 2.605(36)(0.3.18), 5.70(34)(024), 3.173(34)(1.2.14). The IR data are given. Chemical composition (wt%, electron probe, H2O content by the Penfield method): Na2O 16.77, K2O 1.11, CaO 10.73, SrO 1.24, FeO 2.56, MnO 1.00, Ce2O3 0.27, SiO2 50.04, ZrO2 11.90, TiO2 0.67, Cl 1.70, F 011, H2O 1.58, -O=(Cl,F)2 0.43, total 99.25. Empirical formula (based on total of cations Si +Zr+ Ti = 57.7 as determined by crystal structure analysis) is (Na33.30K1.45Sr0.74)Σ35.49(Ca11.77Cc0.10)Σ11.87(Fe2.19Mn0.87)Σ3.06Zr5.94(Ti0.52Si0.260.78 St51O144.48(OH)4.80Cl2.95F0.36·3H2O. Simplified formula: (Na,K,Sr)35Ca12Fe3Zr6TiSi51O144(O,OH,H2O)9Cl3. The mineral is named labyrinthite (from the Greek 'labyrinthos' [labyrinth]) for its unusually complex crystal structure, whose unit cell contains about 800 cations and anions distributed over more than 100 crystallographic sites. The crystal structure is characterized by the presence of two types of modules (alluaivite-like and eudialyte-like) alternating along the triad axis, causing labyrinthite to have a double c period of its unit cell relatively to eudialyte, and a close crystal chemical relationship to rastsvetacvite (ZRMO, 2006, No. 1). According to the authors' crystal chemical systematics of the eudialyte group, the mineral belongs to one of its three principal subgroups characterized by the 24-layered structural array. Labyrinthite is a late-pegmatitic mineral formed during the final stages of hyperagpaitic pegmatite formation. Type material is deposited at the Fersman Mineralogical Museum Moscow.

Revue / Journal Title

Zapiski Vserossijskogo mineralogičeskogo obŝestva    ISSN  0869-6055 

Source / Source

2006, vol. 135, no2, pp. 38-49 [12 page(s) (article)]

Langue / Language

Russe

Editeur / Publisher

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

Localisation / Location

INIST-CNRS, Cote INIST : 4673, 35400014675517.0030

Nº notice refdoc (ud4) : 18813948



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