Crystal chemistry of fluorcarletonite, a new mineral from the Murun alkaline complex (Russia)

Kaneva, Ekaterina; Radomskaya, Tatiana; Suvorova, Ludmila; Sterkhova, Irina; Mitichkin, Mikhail

This paper reports the first description of the crystal structure and crystal chemical features of fluorcarletonite, a new mineral from the Murun potassium alkaline complex (Russia), obtained by means of single-crystal and powder X-ray diffraction (XRD), electron microprobe analysis (EMPA), thermogravimetry (TG), differential scanning calorimetry (DSC), and Fourier transform infrared (FTIR) spectroscopy. The crystal structure of fluorcarletonite, inline-formulaKNa4inline-formulaCa4inline-formulaSi8inline-formulaO18inline-formula(CO3)4(F,OH)⚫ inline-formulaH2O, a rare phyllosilicate mineral, contains infinite double-silicate layers composed of interconnected four- and eight-membered rings of inline-formulaSiO4 tetrahedra and connected through the interlayer K-, Na- and Ca-centered polyhedra and inline-formulaCO3 triangles. The X-ray diffraction analysis confirms the mineral to be tetragonal, inline-formulaP4∕mbm, inline-formulaa=13.219(1) Å, inline-formulac=16.707(2) Å, inline-formulaV=2919.4(6) Åinline-formula3 (powder XRD data), inline-formulaa=13.1808(5) Å, inline-formulac=16.6980(8) Å, inline-formulaV=2901.0(3) Åinline-formula3 (single-crystal XRD data, 100 K). The EMPA (average from 10 analyses) gave the following composition (wt %): inline-formulaSiO2 44.1(6), CaO 20.0(3), inline-formulaNa2O 11.1(3), inline-formulaK2O 4.5(2), F 1.3(5), inline-formulaTiO2 0.1(1) and inline-formulaAl2O3 0.03(3). The TG–DSC analysis confirmed the presence of inline-formulaH2O and inline-formulaCO2 (weight losses of 1.17 % and 14.9 %, respectively). The FTIR spectrum acquired in the range from 4000 to 400 cminline-formula−1 reveals the presence of inline-formulaH2O, inline-formulaCO3 and OH groups. The average formula of fluorcarletonite calculated from the results of EMPA and crystal structure refinement is inline-formulaK1.04inline-formulaNa3.89inline-formulaCa3.87inline-formulaTi0.01inline-formulaSi7.99inline-formulaAl0.01inline-formulaO18(inline-formulaCO3)inline-formula3.86(inline-formulaF0.72OH0.28)inline-formulaRadical⚫1.11inline-formulaH2O.

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Kaneva, Ekaterina / Radomskaya, Tatiana / Suvorova, Ludmila / et al: Crystal chemistry of fluorcarletonite, a new mineral from the Murun alkaline complex (Russia). 2020. Copernicus Publications.

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