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Titre du document / Document title

Zirsilite-(ce), (Na, □)12(Ce, Na)3Ca6Mn3Zr3Nb (Si25O73)(OH)3(CO3) . H2O, and carbokentbrooksite (Na, □)12(Na, Ce)3Ca6Mn3Zr3Nb(Si25O73)(OH)3(CO3) . H2O: Two new eudialyte group minerals from Dara-I-Pioz alkaline massif, Tajikistan

Auteur(s) / Author(s)


Résumé / Abstract

Zirsilite-(Ce) (ZIR) and carbokentbrooksite (CAR) are two new minerals of the eudialyte group discovered in Dara-i-Pioz alkaline massif, Tajikistan. They have been found in the quartz core of a zonal pegmatite. Associatedminerals are quartz, microcline, aegirine, stillwellite-(Ce), ekanite, polylithionite, pyrochlore, fluorite, calcite and galena. The minerals occur as zonal rhombohedral crystals up to 1-2 cm across size, with the core composed of CAR and the ZIR rim. The color of ZIR is creamy, and CAR is yellow. Other physical properties of the minerals are similar. They are transparent with vitreous luster and white streak; both are brittle, non-fluorescent under UV light. Mohs' hardness 5. Cleavage or parting not observed. Fracture conchoidal. D (meas.) is 3.15(2) g/cm3 for ZIR and 3.14(2) g/cm3 for CAR. D (calc.) is 3.10 g/cm3 for both minerals. They are uniaxial negative wit ω = 1.648(2), E = 1.637(2) for ZIR and ω = 1.645(2), s = 1.635(2) for CAR. They are trigonal, R3m. For ZIR a = 14.248(2) Å, c = 30.076(6) A, V = 5288(4) Å3 And for CAR a = 14.239(3) Å, c = 30.039(8) Å, V = 5288(4) Å3, Z = 3. Strongest XRD lines [d in A (I)] for ZIR: 3.220(100), 2.979(95), 2.857(66), 3.166(56), 4.32(51), 3.975(37), and for CAR: 2.849(100), 2.970(83), 3.204(38), 3.155(35), 3.019(34), 2.590(30). Chemical composition of the minerals (ZIR/CAR, wt. %): Na2O 9.54/10.17, K2O 0.45/0.51, CaO 10.52/10.61, SrO 1.35/1.42, FeO 1.89/2.22, MnO 5.67/5.41, La2O3 2.31/1.79, Ce2O3 3.78/2.97, Nd2O3 0.82/0.76, Pr2O3 0.28/0.24, Y2O3 0.47/0.43, SiO2 45.63/45.55, TiO2 0.45/0.41, ZrO2 10.48/11.07, Nb2O3 3.76/3.55, Cl 0.32/0.29, H2O 1.52/1.18, CO2 0.58/0.78, -O = Cl2 0.07/0.06, total 99.75/99.30. Empirical formulae were calculated on the base of Si = 25.0, and idealized formulae (Z = 3) are: zirsilite-(Ce) - (Na,□)12(Ce,Na)3Ca6Mn3Zr3NbtSi23O73)(OH)3(CO3).H2O, and the quite similar for CAR - (Na,□)12(Na,Ce)3Ca6Mn3Zr3Nb (Si25O73)(OH)3(CO3).H2O. The main difference between these minerals is the dominance of REE(Ce) over Na in N(4) site of ZIR. Comparative data for kentbrooksite, the nearest analogue of the two new minerals, are given. According to the single-crystal analyses, ZIR and CAR are isostructural with kentbrooksite - Na12(Na,REE)3(Ca,REE)6Mn3Zr3Nb (Si23O73)[O(H2O)2]F2. Their names reflect their compositional and structural features.

Revue / Journal Title

Zapiski Vserossijskogo mineralogičeskogo obŝestva    ISSN  0869-6055 

Source / Source

2003, vol. 132, no5, pp. 40-51 [12 page(s) (article)]

Langue / Language


Editeur / Publisher

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

Localisation / Location

INIST-CNRS, Cote INIST : 4673, 35400011463735.0040

Nº notice refdoc (ud4) : 15861098

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