X-ray single-crystal and optical spectroscopic study of chromian pumpellyite from Sarany, Urals, Russia




    • NAGASHIMA Mariko
    • Mineralogical Crystallography, Institute of Geological Sciences, University of Bern
    • AKASAKA Masahide
    • Department of Materials Creation and Circulation Technology, Graduate School of Science and Engineering, Shimane University
    • IKEDA Ko
    • Department of Advanced Materials Science and Engineering, Yamaguchi University
    • KYONO Atsushi
    • Division of Earth Evolution Sciences, Graduate School of Life and Environmental Sciences, University of Tsukuba


The crystal structure of a chromian pumpellyite K<sub>0.03</sub>Na<sub>0.07</sub>Ca<sub>7.82</sub>Mn<sup>2+</sup><sub>0.01</sub>Mg<sub>1.95</sub>Fe<sup>3+</sup><sub>0.05</sub>V<sup>3+</sup><sub>0.01</sub>Cr<sup>3+</sup><sub>3.77</sub>Al<sub>6.52</sub>Ti<sub>0.02</sub>Si<sub>11.82</sub>O<sub>42.06</sub>(OH)<sub>13.94 </sub>(<i>Z</i> = 1) from Sarany in the Russian Urals was studied using optical spectroscopy and single-crystal X-ray diffraction methods. Five discrete peaks were observed in an optical spectrum. Of these, three at 392(<i>υ</i><sub>2</sub>), 574(<i>υ</i><sub>1</sub>) and 726 nm were attributed to Cr<sup>3+</sup>; one at 456 nm to Fe<sup>3+</sup>; and a peak at 291 nm is related to <i>M</i>-O charge transfer. The crystal field parameters determined here (<i>B</i>, <i>C</i> and 10<i>Dq</i>) give 94% ionic character of Cr-O bonds and a mean <sup>VI</sup><i>M</i>-O distance of 1.954 Å. The crystal structure of chromian pumpellyite with <i>a</i> = 8.809(3), <i>b</i> = 5.9330(9), <i>c</i> = 19.137(1) Å, <i>β</i> = 97.606(2)° at 90 K, and <i>a</i> = 8.807(6), <i>b</i> = 5.943(4), <i>c</i> = 19.18(1) Å, <i>β</i> = 97.44(2)° at 293 K was refined using 1297 unique reflections measured at 90 K, converging at <i>R</i> = 2.3%. Site occupancies of the main constituent elements at the two independent octahedral <i>X</i> and <i>Y</i> sites are <i>X</i> = 0.49Mg + 0.308Cr + 0.202Al and <i>Y</i> = 0.742Al + 0.258Cr. Although Cr<sup>3+</sup> ions occupy both the <i>X</i> and <i>Y</i> sites, the site preference of chromium for the <i>X</i> site is stronger than that for the <i>Y</i> site, as indicated by the distribution coefficient of chromium between the <i>X</i> and <i>Y</i> sites, <i>K</i><sub>D</sub> = (Cr/Al)<sub><i>X</i></sub>/(Cr/Al)<sub><i>Y</i></sub>, of 4.39. The substitution of Cr<sup>3+</sup> for Al in the <i>Y</i> site directly results in structural changes, whereas that in the <i>X</i> site is not effective for structural change.


  • Journal of mineralogical and petrological sciences

    Journal of mineralogical and petrological sciences 105(4), 187-193, 2010-08-01

    一般社団法人 日本鉱物科学会

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