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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

Published online by Cambridge University Press:  02 January 2018

Atali A. Agakhanov
Affiliation:
Department of Crystallography, St. Petersburg State University, University Embankment 7/9, St. Petersburg, 119034 Russia Fersman Mineralogical Museum, Russian Academy of Sciences, Leninskii Pr-t, 18-2, Moscow, 117071 Russia
Leonid A. Pautov
Affiliation:
Fersman Mineralogical Museum, Russian Academy of Sciences, Leninskii Pr-t, 18-2, Moscow, 117071 Russia
Elena Sokolova*
Affiliation:
Department of Geological Sciences, University of Manitoba, Winnipeg, Manitoba, R3T 2N2, Canada
Frank C. Hawthorne
Affiliation:
Department of Geological Sciences, University of Manitoba, Winnipeg, Manitoba, R3T 2N2, Canada
Vladimir Yu Karpenko
Affiliation:
Fersman Mineralogical Museum, Russian Academy of Sciences, Leninskii Pr-t, 18-2, Moscow, 117071 Russia
Oleg I. Siidra
Affiliation:
Department of Crystallography, St. Petersburg State University, University Embankment 7/9, St. Petersburg, 119034 Russia
Viktor K. Garanin
Affiliation:
Fersman Mineralogical Museum, Russian Academy of Sciences, Leninskii Pr-t, 18-2, Moscow, 117071 Russia
*

Abstract

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 khvorovite, mendeleevite-(Ce), sokolovaite, hyalotekite, orlovite, kirchhoffite, pekovite, neptunite, zeravshanite, senkevichite, nordite-(Nd), alamosite, pyrochlore-group minerals and baratovite. Mendeleevite-(Nd) forms colourless cubic crystals 10–40 μm in size; it has a vitreous lustre and a 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 Pm3̄, a = 21.9106(4) Å; Z = 2. The six strongest reflections in the powder X-ray diffraction pattern are [d (Å), I (%), (h k l)] 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) apfu, with F + OH + H2O = 35 pfu, is Cs6(□4.20K1.80)∑6{[(Nd9.57Ce6.13Sm2.39La2.20Pr1.68Gd0.93Eu0.27)∑23.17(Ca3.90Sr2.87)∑6.77]∑29.940.06}∑30(Si70.03O175)(OH14.47F6.54)∑21.01 (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.

Type
Research Article
Copyright
Copyright © The Mineralogical Society of Great Britain and Ireland 2017

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