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Infrared investigation of CO2-bearing cordierites

Abstract : CO2 molecules were introduced experimentally into the structural channels of synthetic well ordered Mgcordierite (Mg2[VI][(Al4Si5)[IV]O18]) at temperatures of 600 and 800° C, and pressures of 7, 8, 10, 12, and 25 kbar. Powder infrared spectra of the run products show five absorption bands in the region of the asymmetric stretching mode of CO2. Two of them, strong and sharp, occurring at 2353 cm−1 {2} and 2348 cm−1 {3}, are related to two different types of CO2 molecules. The relative intensity of the band {2} (type I) increases with the cell parameter co whereas the relative intensity of the band {3} (type II) increases with the parameter a0 of the crystal. It is concluded that CO2 molecules of type I may be oriented with their elongation parallel to the c-axis of the crystal, while CO2 molecules of type II lie with their O-C-O vector parallel to the a-axis. Analytical data indicate that the intensity ratio Z of these two bands ({2}/{3}) is a linear function of the CO2 content of cordierite. This ratio depends also on the temperature and, to a less extent, on the pressure under which cordierite entrapped CO2 molecules. It is proposed to combine this infrared parameter Z together with an estimate of the P-T conditions of the incorporation of CO2 into the channels, in order to determine the CO2 content of natural cordierites. The samples do not need to be of high purity and only small amounts (<5 mg) are necessary. This semi-empirical analytical method, which does not require complicated data treatments, is suitable for CO2-rich cordierites of granulite facies rocks.
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Submitted on : Tuesday, January 23, 2018 - 5:02:32 PM
Last modification on : Wednesday, January 31, 2018 - 3:30:58 PM

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Nicole Le Breton. Infrared investigation of CO2-bearing cordierites. Contributions to Mineralogy and Petrology, Springer Verlag, 1989, 103 (3), pp.387 - 396. ⟨10.1007/BF00402923⟩. ⟨insu-01691214⟩

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