http://www.ingentaconnect.com/content/minsoc/mag/pre-prints/content-minmag-1252Agakhanov, Atali A.; Pautov, Leonid A.; Sokolova, Elena; Hawthorne, Frank C.; Karpenko, Vladimir Yu.; Siidra, Oleg. I.; Garanin, Viktor K. - Mendeleevite-(Nd), (Cs,□)6(□,Cs)6(□,K)6(REE,Ca)30(Si70O175)(OH,H2O,F)35, a new mineral from the Darai-Pioz alkaline massif, Tajikistan - Mineralogical Magazine ~[PREPUBLICATION 19 Feb. 2016]
Mendeleevite-(Nd), (Cs,□)6(□,Cs)6(□,K)6(REE,Ca)30(Si70O175)(OH,H2O,F)35 is a new mineral from the Darai-Pioz alkaline massif, Tajikistan. Mendeleevite-(Nd) was found in a pectolite aggregate in silexites (quartz-rich rocks) which consist of fine to medium pectolite grains, quartz, aegirine and fluorite, with minor are khvorovite, mendeleevite-(Ce), sokolovaite, hyalotekite, orlovite, kirchhoffite, pekovite, neptunite, zeravshanite , senkevichite, nordite-(����), alamosite, pyrochlore-group minerals and baratovite. Mendeleevite-(Nd) forms colorless cubic crystals 10–40 μm in size; it has a vitreous lustre and the Mohs’ hardness of 5–5.5; Dmeas. = 3.20(2) g/cm3, Dcalc. = 3.155 g/cm3. Mendeleevite-(Nd) is optically isotropic, with the refractive index n = 1.582(2). Mendeleevite-(Nd) is cubic, space group Pm⎯3, a = 21.9106(4) Å; Z = 2. The six strongest reflections in the X-ray powder diffraction pattern are ~[d (Å), I (%), (hkl)] are: 11.01, 100, (0 0 2); 15.63, 55 (0 1 1); 3.47, 42, (2 0 6); 3.099, 42, (3 4 5); 2.192, 42, (0 0 10); 1.819, 41, (3 6 10). Chemical analysis by electron microprobe gave SiO2 42.30, Ce2O3 10.12, La2O3 3.60, Nd2O3 16.19, Pr2O3 2.79, Sm2O3 4.19, Gd2O3 1.69, Eu2O3 0.47, SrO 2.99, CaO 2.20, Cs2O 8.50, K2O 0.85, H2O 3.85, F 1.25, –O=F2 –0.53, sum 100.46.wt. %, with H2O calculated by analogy with mendeleevite-(Ce). The empirical formula based on 210 (O + F) a.p.f.u., with F + OH + H2O = 35 p.f.u., is Cs6(□4.20K1.80)Σ6{~[(Nd9.57Ce6.13Sm2.39La2.20Pr1.68Gd0.93Eu0.27)Σ23.17 (Ca3.90Sr2.87)Σ6.77]Σ29.94□0.06}Σ30(Si70.03O175)(OH14.47F6.54) Σ21.01(H2O)14, Z = 2. The simplified and ideal formulae are (Cs,□)6(□,Cs)6(□,K)6(REE,Ca)30(Si70O175)(OH,H2O,F)35 and Cs6(REE23Ca7)(Si70O175)(OH,F)19(H2O)16, respectively. The compatibility index (from measured density) = –0.039 (excellent). Mendeleevite-(Nd) is a Nd analogue of mendeleevite-(Ce), (Cs,□)6(□,Cs)6(□,K)6(REE,Ca,□)30(Si70O175)(H2O,OH,F,□)35. Both minerals are named after Dmitri Mendeleev (1834–1907), the great Russian chemist, author of the periodic table of chemical elements, who has had a significant impact on the development of natural sciences and industry, both in Russia and around the world.
Thema: Mendeleevite-(Nd) (Gelesen 2323 mal)
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