Phase diagrams of (Mg, Fe)₂ Si O₄. From top down: density, bulk modulus, saturation water content, and thermal expansion coefficient as functions of temperatureand pressure calculated from Eqs. (39) and (B.2). Shown are the Fe free case, that is ξ_Fe = 0 (left) and ξ_Fe = 0.25 (right). The dependence of the phase transitions on the Fe and water content are neglectedhere. The pressure and temperature range in the plot roughly marks the validity range of the model fit. We note that we have assumed a stability field of the γ-phase of up to ≲30 GPa, which overestimates the dissociation pressure of Ringwoodite. We imposed this assumption to ensure that our model yields strict upper bounds on the water content.