Fluorellestadite from burned coal dumps: crystal structure refinement, vibrational spectroscopy data and thermal behavior

• Published in: Mineralogy and petrology 2021-06, Vol.115 (3), p.271-281
• Main Authors: Avdontceva, Margarita S., Zolotarev, Andrey A., Krivovichev, Sergey V., Krzhizhanovskaya, Maria G., Sokol, Ella V., Kokh, Svetlana N., Bocharov, Vladimir N., Rassomakhin, Mikhail A., Zolotarev, Anatoly A.
• Format: Article
• Language: English
• Subjects: Ambient temperature; Analytical methods; Apatite; Coal; Crystal structure; Crystals; Earth and Environmental Science; Earth Sciences; Fluorapatite; Fluorine; Geochemistry; Infrared analysis; Infrared spectroscopy; Inorganic Chemistry; Mineralogy; Original Paper; Raman spectroscopy; Single crystals; Spectroscopy; Spectrum analysis; Statistical methods; Temperature; Tetrahedra; Thermal expansion; Thermodynamic properties; Unit cell; X rays; X-ray diffraction; X-ray diffraction analysis
• ISSN: 0930-0708; 1438-1168
• DOI: 10.1007/s00710-021-00740-4

Nine different samples of fluorellestadite from Chelyabinsk, Kizel and Kuznetsk coal basins were studied by single-crystal X-ray diffraction analysis, thermal X-ray diffraction (25–800 °C), Infrared (IR) and Raman spectroscopy. Fluorellestadite is hexagonal, space group P 6 3 / m, the unit-cell parameters for the nine samples studied vary within rather small ranges: a  = 9.415(5) – 9.4808(7) Å, c  = 6.906(2) – 6.938(8) Å, V  = 530.3(4) – 538.41(9) Å 3 . The mineral is isotypic with apatite, the structure is based upon isolated T O 4 tetrahedra, where the T position is statistically occupied by Si 4+ and S 6+ with the ideal ratio Si:S equal to 1:1. The fluorine atoms are located in channels of the Ca 4 [(S,Si)O 4 ] 6 framework oriented parallel to the c axis. The thermal expansion of fluorellestadite is almost isotropic in the temperature range 25–800 °C (for ambient temperature: α a  = 12.0·10 −6  °C −1 , α c  = 11.9·10 −6  °C −1 ; for 800 °C: α a  = 18.2·10 −6  °C −1 , α c  = 18.6·10 −6  °C −1 ). A similar thermal behavior had been observed for fluorapatite. Despite the same structure motifs and close conditions of formation, the samples of fluorellestadite show different S/Si/P occupancies for T site and the F/Cl/OH ( X -position) ratios.