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Titre du document / Document title

Na27K8Ca12Fe3-, Zr6Si4[Si3O9]4[Si9O27]4(O, OH, H2O), Cl2, a new mineral with a modular eudialyte-like structure and crystal-chemical systematics of the eudialyte group

Auteur(s) / Author(s)

KHOMYAKOV A. P. ; NECHELWSTOV G. N. ; ARAKCHEEVA A. V. ; RASTSVETAEVITE ;

Résumé / Abstract

Rastsvetaevite was found on Mt. Rasvumchorr (Khibiny alkaline massif, Kola peninsula) occurring in a hypcragpaitic pegmatite as irregularly shaped grains 1-2 mm in size and their aggregates, up to 2 cm across. It is associated with nepheline, sodalite, potassium feldspar, aegirine, scherbakovite, villiaumitc, natrite, nacaphite, rasvumite, etc. Color reddish-pink, transparent, conchoidal fracture; brittle; luster vitreous; streak white. Mohs' hardness 5-6. Dmens= 2.86(2) g/cm3 (volumetric method), Dcalc = 2.84 g/cm3. Optically uniaxial, positive, n,, = = 1.598(1), ne = 1.600(1). Trigonal, space group R3m, a = 14.249(1), c = 60.969(7) A, V= 10720(3) Å3. Z= 3. The strongest lines of the powder diffraction pattern [d, Å (I)(hkl)] arc: 2.987(100)(3.1.10), 4.345(81)(2.0.10). 2.861 (73)(408), 3.249(57)(2.0.16), 6.48(47)(108), 3.565(41)(220). IR data arc given in the paper. Chemical composition (wt %, electron probe, H2O content by Penfield method): Na2O 13.76, K2O 6.12, CaO 10.37, SrO 1.26, BaO0.07, FeO2.73, MnO 0.49. Cc2O30.11, Al2O30.17, SiO2 50.72, ZrO211.48, HfO20.14, TiO20.39, Nb2O5 0.34, Ta2O5 0.05, Cl 1.33, H2O 0.89. -O = Cl2 0.30; total 100.12. Empirical formula (based on total of anions 152.0, Z= 3) is Na27 10(K7.93Ba0.037 .96 (Ca11.29Sr0.74Cc0.04)Σ12.07(Fe2.32Mn0.42)Σ2.74 (Zr5.69Ti0,3Hf0.04)Σ6. 03 (Sι51 53 Al0.020Nb0.16Ta0.0151.90O2.114(OH)1.86Cl2.291.71H2O. Simplified formula: Na27K8Ca12Fe3Zr6Si52,O144(O,OH, H2O)6Cl2 or Na27K8Ca12Fe3Zr6Si4[Si3O9]4[Si9O27]4(O2,OH2H2O)6Cl2. Crystal structure of the mineral includes two types of modules (alluaivitc-likc and eudialyte-like) alternating along the c axis, and causing rastsvetacvite to have a double c period (relative to eudialyte) and pronounced ion-exchange properties. In crystal chemical systematics of eudialyte-group minerals rastsvctaevite forms a subgroup, one among three principal ones characterized by the 24-layered structural array. Rastsvetaevite is a late pegmatite mineral, the product of natural transformation of eudialyte. It is widespread in margins of Khibiny apatite deposits, in zones marked by intensive potassium metasomatism with replacement of standard eudialytc by its K-rich analogues. The mineral is named in honor of Ramiza K. Rastsvetaeva (b. 1936), prominent Russian crystallographer, who has deciphered crystal structures for many newly discovered minerals, including the above one. The 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, no1, pp. 49-65 [17 page(s) (article)]

Langue / Language

Russe

Editeur / Publisher

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

Localisation / Location

INIST-CNRS, Cote INIST : 4673, 35400014675459.0040

Nº notice refdoc (ud4) : 18813995



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