Static elasticity of cordierite II: effect of molecular CO2 channel constituents on the compressibility

Two natural CO₂-rich cordierite samples (1.00 wt% CO₂, 0.38 wt% H₂O, and 1.65 wt% CO₂, 0.15 wt% H₂O, respectively) were investigated by means of Raman spectroscopy and single-crystal X-ray diffraction at ambient and high pressures. The effect of heavy-ion irradiation (Au 2.2 GeV, fluence of 1 × 10¹² ions cm^?2) on the crystal structure was investigated to characterize the structural alterations complementary to results reported on hydrous cordierite. The linear CO₂ molecules sustained irradiation-induced breakdown with small CO₂-to-CO conversion rates in contrast to the distinct loss of channel H₂O. The maximum CO₂ depletion rate corresponds to ~12 ± 5 % (i.e. ~0.87 and ~1.49 wt% CO₂ according to the two samples, respectively). The elastic properties of CO₂-rich cordierite reveal stiffening due to the CO₂ molecules (non-irradiated: isothermal bulk modulus K ₀ = 120.3 ± 3.7 GPa, irradiated: K ₀ = 109.7 ± 3.7 GPa), but show the equivalent effect of hydrous cordierite to get softer when irradiated. The degree of anisotropy of axial compressibilities and the anomalous elastic softening at increasing pressure agrees with those reported for hydrous cordierite. Nevertheless, the experimental high-pressure measurements using ethanol–methanol reveal a small hysteresis between compression and decompression, together with the noticeable effect of pressure-induced over-hydration at pressures between 4 and 5 GPa.