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Titre du document / Document title

DUALITE, Na30(Ca,Na,Ce,Sr)12 (Na,Mn,Fe,Ti)6Zr3Ti3MnSi53O144(OH2H2OCl)9, A NEW ZIRCONO-TITANOSILICATE WITH A MODULAR EUDIALYTE-LIKE STRUCTURE FROM LOVOZERO ALKALINE MASSIF, KOLA PENINSULA, RUSSIA

Auteur(s) / Author(s)

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

Résumé / Abstract

Dualite was found on Mt. Alluaiv (Lovozero massif. Kola Peninsula), in hyperagpaitie pegmatoidrock as rare anhedral grains up lo 0.3-0.5 mm across. Associated minerals are : sodium-potassium feldspar, nepheline, sodali(c, cancrinite, aegirine, alkaline amphibole, eudialyte, lovozerite, lomonosovite, vuonneimite, lamprophyllite, sphalerite and villiaumite. It is yellow, transparent or translucent, with conchoidal fracture; brittle; luster vitreous; streak while. Mohs' hardness 5. D(meas.) = 2.84(3) g/cm (volumetric method), D(cale.) = 2.814 g/cm3. The mineral dissolves and gelatinises in acid at room temperature. Non-fluorescent. Optically uniaxial, positive, no = 1.610(1), ne= 1.613(1). Trigonal, space group R3m, a = 14.153(9), e = 60.72(5) Å, V= 10533(27) Å3, Z= 3. The strongest lines of the powder diffraction pattern [d, Å(I)(hkl)] are 7.11(40)(110), 4.31(50)(0.2.10), 2.964(10())(1.3.10), 2839(90)(048), 2.159(60)(2.4.10. 0.4.20), 1.770(60)(2.4 22, 4.0.28, 440), 1.362(50) (5.5.12. 3.0.42). Chemical composition (wt, %, electron probe, H2O content from crystal structure analysis); Na20 17.74, K2O 0.08, CaO 8.03. SrO 1.37, BaO 0.29, MnO 2.58, FeO 1.04, La2O30.79, CeO3, 1.84, Nd2O30.88, Al2O30.20, Sio2 51.26, TiO24.40, ZrO25.39, Nb2O5 1.94, Cl 0.58, H2O 1.39, O = Cl2 0.13, CYMMa 99.67. Empirical formula (based on Σcations = 106 apfu as determined by crystal structure analysis) is (Na29.79.Ba0.1K0.10)30(Ca8.55Na1.39REE1.27Sr0.79)12 (Na3.03 Mn 1.35Fe2+0.87Ti0.77)6 (Zr2.61Nb0.39 )9 (Ti2.52Nb0.48)3(Mn0.82Si0.18)1 (Si50.27Al0.25)51 O144(OH)6.54(H2O)1.34. Cl0.98]8.86 Simplified formula: Na30(Ca,Na,Ce,Sr)12(Na,Mn,Fe,Ti)6Zr3Ti3 MnSi51O144(OH,H2O,Cl)9. The name dualite is derived from the Latin «dualis» [dual] in allusion to the dual taxonomie membership of the mineral, which is at once a zirconosilicate and titanosilicate. The crystal structure is characterized by the presence of two types of modules (alluivite-like and cudialyte-like) alternating along the triad axis, causing dualite to have double c period relative to eudialytc and a close crystal chemical relationship to rastsvetaevite (ZRMO, 2006, N 1) and labyrynthite (ZRMO, 2006, N2). According to the authors' crystal chemical systematics of the eudialytc group, the mineral belongs to one of its three principal subgroups characterized by a 24-layered structural array, Dualite is a lale-pegmatitie mineral formed during the final stages of hyperagpaitie pegmatite formation. Type material is deposited at the Fersman Mineralogical Museum, Moscow.

Revue / Journal Title

Zapiski Vserossijskogo mineralogičeskogo obŝestva    ISSN  0869-6055 

Source / Source

2007, vol. 136, no4, pp. 31-42 [12 page(s) (article)]

Langue / Language

Russe

Editeur / Publisher

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

Localisation / Location

INIST-CNRS, Cote INIST : 4673, 35400019807172.0040

Nº notice refdoc (ud4) : 20451408



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