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In this work, we address the intensity evolution of the CO2 FTIR bands of cordierite as a function of increasing T, by comparing data obtained from in situ versus quenching measurements. A natural well-characterized cordierite from Kragero (Arendal region, Norway) was studied up to 1200 °C using a heating stage fitted on a FTIR microscope. Two different oriented sections (001) and (010), respectively, were examined in order to check for the effect of the channel orientation on the CO2 release from the matrix. Spectra collected in situ show that increasing temperatures induces an increase in peak width for all CO2-related bands. The effects on the integrated absorbance A i are different for the different modes. Most notably, the integrated intensity A i of the anti-symmetric stretching mode (ν3) increases significantly up to 800 °C and then progressively decreases to 1000/1200 °C, depending on the sample orientation. Data obtained on quenched samples reveal that there is no variation in the band intensity for T

We report a FTIR (Fourier transform infrared) study of a set of cordierite samples from different occurrence and with different H2O/CO2 content. The specimens were fully characterized by a combination of techniques including optical microscopy, single-crystal X-ray diffraction, EMPA (electron microprobe analysis), SIMS (secondary ion mass spectrometry), and FTIR spectroscopy. All cordierites are orthorhombic Ccmm. According to the EMPA data, the Si/Al ratio is always close to 5:4; X Mg ranges from 76.31 to 96.63, and additional octahedral constituents occur in very small amounts. Extraframework K and Ca are negligible, while Na reaches the values up to 0.84 apfu. SIMS shows H2O up to 1.52 and CO2 up to 1.11 wt%. Optically transparent single crystals were oriented using the spindle stage and examined by FTIR micro-spectroscopy under polarized light. On the basis of the polarizing behaviour, the observed bands were assigned to water molecules in two different orientations and to CO2 molecules in the structural channels. The IR spectra also show the presence of small amounts of CO in the samples. Refined integrated molar absorption coefficients were calibrated for the quantitative microanalysis of both H2O and CO2 in cordierite based on single-crystal polarized-light FTIR spectroscopy. For H2O the integrated molar coefficients for type I and type II water molecules (ν3 modes) were calculated separately and are [I]e = 5,200 ± 700 l mol−1 cm−2 and [II]e = 13,000 ± 3,000 l mol−1 cm−2, respectively. For CO2 the integrated coefficient is $$ \varepsilon_{{{\text{CO}}_{ 2} }} $$ = 19,000 ± 2,000 l mol−1 cm−2.

In this study, we describe the first FTIR measurements of CO2 desorption from cordierite, a microporous mineral stable up to high T conditions. To this purpose, we collected isothermal heating data on several (001) oriented sections of a well-characterized CO2-rich sample. Single-crystal slabs were heat-treated up to 1000 °C, and the intensity of the ν 3 antisymmetric stretching mode of CO2 at 2348 cm−1 was monitored as a function of time. The experimental data were modeled by using the mono-dimensional plane-sheet diffusion formalism; diffusion coefficients were plotted in the Arrhenius space and activation energies were calculated. Final data are as follows: −logD 0 = 4.2 ± 0.5 m2/s and E a = 208 ± 11 kJ/mol. Comparison with diffusion data from the literature (Lepezin and Osorgin in Rossijskaa Akademia Nauk 339:658–661, 1994) shows that at 800 °C H2O diffuses almost two orders of magnitude faster than CO2 along the structural channels of cordierite, with the difference in diffusion coefficients increasing at lower temperatures, and this implies that at lower temperatures H2O mobility is more favored compared to CO2. Therefore, the volatile contents measured in exhumed rocks may not reflect the H2O/CO2 ratio upon cordierite crystallization, and this could significantly affect the thermodynamic calculations for fluid activities or peak metamorphic conditions.

The crystal chemistry of sekaninaite from Dolní Bory, Czech Republic, was characterized by a multimethod approach. Particular emphasis was put on the characterization of the channel constituents (i.e. H2O and CO2). Electron microprobe analysis shows the sample to be close to the Fe endmember [XFe = Fe/(Fe+Mg) = 94%) with significant Mn (1.48 wt.%) present; laser ablation mass-spectrometry showed the presence of 0.42 wt.% Li2O. H2O and CO2 contents (1.48 and 0.17 wt.%, respectively) were determined via secondary-ion mass-spectrometry. Sample homogeneity was checked by Fourier-transform infrared (FTIR) imaging using a microscope equipped with a focal plane array detector. Single-crystal FTIR spectroscopy confirmed the presence of two types of H2O groups in different orientations (with prevalence of the type II orientation), and that CO2 is oriented preferentially normal to the crystallographic c axis. Using the Beer-Lambert relation, integrated molar coefficients, εi, were calculated for both types of H2O (εi H2O[I] = 6000±2000; εi H2O[II] = 13000±1000) and for CO2 (εiCO2 = 2000±1000).