Fig. 5

Aggregate properties of δ-(Al,Fe)OOH at room conditions plotted as a function of the Fe/(Al + Fe) molar ratio. Adiabatic aggregate moduli and velocities are shown in (a, b), respectively. In (a), literature data are shown as solid squares, and circles are results from Wang et al. (2022) and Satta et al. (2024), respectively. Open stars are the results for ε-FeOOH by Ikeda et al. (2019) and were not considered in the fit. Solid lines are linear fits to observations within the investigated compositional range, while dashed lines extrapolate linear fits toward higher Fe contents. In (b), solid symbols are values determined from single-crystal experimental data, with solid squares and circles used to plot literature results from Wang et al. (2022) and Satta et al. (2024), respectively. Open symbols are values from Brillouin experiments on polycrystalline samples, with squares and diamonds showing the results by Mashino et al. (2016) and Su et al. (2021) respectively