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Open Access item Thermal X-ray Diffraction Study of Chaorite from Russia

Authors:Matesanz, Emilio
García-Guinea, Javier
Crespo Feo, Elena
López-Arce, Paula
Valle Fuentes, Francisco José
Correcher, Virgilio
Keywords:Charoite, Structure, Dehydration, X-ray Diffraction, Differential thermal analysis, Thermogravimetry, Thermoluminescence
Issue Date:2008
Publisher:Mineralogical Association of Canada
Citation:Canadian Mineralogist (2008) [in press]
Abstract:The effect of thermal annealing of charoite silicate K5 Ca8 (Si6O15) (Si2O7) (Si4O9) (OH)·3H2O have been studied by X-ray diffraction (XRD), differential thermal analysis (DTA), thermogravimetry (TG) and thermoluminescence (TL). The chemical composition, analysed under electron probe micro-analysis (EPMA), indicates significant amounts of Na, Ba, Fe and F and the environmental scanning electron microscope (ESEM) results show impurities of unusual minerals such as tinaksite and aegirine. The cell parameters of both natural and preheated charoite, determined by XRD, are (i) a=[Å] 19.786(2); b=[Å] 32.003(3); c=[Å] 7.8565(9); α=90º; β=97.159º; γ=90º with a Snyder FOM of 7.1932 for the non-annealed sample and (ii) a=[Å] 19.567(2); b=[Å] 31.821(3); c=[Å] 7.1171(7); α=90º; β=94.000º(2); γ=90º; Snyder's FOM 6.2637 for the preheated charoite. The thermal effect supposes an axes shortening, of Δa=0.219[Å](2); Δb=0.182 [Å]; Δc=0.7394 [Å] and the β angle tilts only 3.159º. The DTA-TG and TL emission suggest: (i) a thermal gap of 80ºC-290ºC explained by charoite dehydration of different types of waters, i.e. hydrogen-bonded to the charoite lattice and non-bonded waters and (ii) the gap 290ºC-480ºC depicting a dehydroxylation processes.
Description:19 pages, 4 figures.-- To be published in Canadian Mineralogist.
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