Carbon incorporation in plumbogummite-group minerals

Ian Grey, F Shanks, N Wilson, W G Mumme, William Birch

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Non-stoichiometric, carbon-containing crandallite from Guatemala and plumbogummite from Cumbria have been characterized using electron microprobe (EMPA) and wet-chemical analyses, Rietveld analysis of powder X-ray diffraction (PXRD) patterns, and infrared (IR), Raman and cathodoluminescence (CL) spectroscopies. The samples contain 11.0 and 4.8 wt. CO2, respectively. The IR spectra for both samples show a doublet in the range 1410-1470 cm(-1), corresponding to CO3 vibrations. Direct confirmation of CO3 replacing PO4 was obtained from difference Fourier maps in the Rietveld analysis. Carbonate accounts for 67 of the C in the plumbogummite and 20 of the C in the Guatemalan crandallite, the remainder being present as nano-scale organic carbon. The CO3 substitution for PO4 is manifested in a large contraction of the tetrahedral volume (14-19 ) and by a contraction of the a axis, analogous to observations for carbonate-containing fluorapatites. Stoichiometric crandallite from Utah was characterized using the same methods, for comparison with the non-stoichiometric, carbon-bearing phases.
Original languageEnglish
Pages (from-to)145 - 158
Number of pages14
JournalMineralogical Magazine
Issue number1
Publication statusPublished - 2011

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