Chlorine-hydroxyl diffusion was measured in pargasitic amphibole from Yunnan province, China at 1.0 GPa, 625 to 800 °C. Experiments were performed by immersing unoriented crystals in water-bearing NaCl in a piston cylinder for durations from 100 to 454 h. Diffusion profiles were on the order of greater than tens of micrometers in length, and electron microprobe analysis allow us to extract semi-quantitative diffusivities from these experiments. The preliminary diffusion coefficients for chlorine in amphibole in the water-bearing experiments are 2.6 × 10⁻¹⁶ m²/s at 625 °C, 4.9 × 10⁻¹⁶ m²/s at 650 °C, 7.6 × 10⁻¹⁶ m²/s at 700 °C, 1.8 × 10⁻¹⁵ m²/s at 750 °C, 2.8 × 10⁻¹⁵ m²/s at 800 °C. For temperatures between 625 and 800 °C, the Arrhenius relation for chlorine-hydroxyl diffusion has an activation energy of 106.6 ± 7.8 kJ/K mol and a D₀ of 4.53 (+7.3, −2.8) × 10⁻¹⁰ m²/s. Our measurements do not show evidence of anisotropy in the diffusion of Cl-OH into amphibole, but future experiments need to better investigate this possibility.

The structural chemistry of carbonates under mantle conditions facilitates our understanding of carbon recycling pathways in the earth’s interior. It also has impacts on the dynamics of mantle–slab interactions. Aragonite is a common calcium carbonate mineral in pelagic marine sediments. The structural chemistry of single-crystal aragonite during successive compression and the behavior of a structural H⁺ have been investigated by micro-vibrational spectroscopy and synchrotron X-ray diffraction techniques in diamond anvil cells. We describe a reduction of the b-axial compressibility beginning at ~15 GPa, and the related discontinuities in the first-order derivatives of the vibrational modes. The structural modifications of aragonite are manifested by mutations occurring in the pressure relations of the wavenumbers of the O-C-O bending modes, and of the bandwidth and band intensities of the measured internal and external modes. These anomalies are indicative of changes occurring in the force constant of the C-O bonds, and possibly a second-order phase transition. Besides, the [CaO₉] polyhedra begin to deform, possibly with some Ca-O bonds becoming elongated and the others shortening. An increase in the co-ordination number for the Ca²⁺ sites could be expected under higher pressures. Additionally, the weakening of the OH modes may imply H⁺-loss from the aragonite lattice above 11.5 GPa.