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The viscosity of CaMgSi₂O₆ (diopside) liquid has been determined up to 13GPa and 2200°C using in situ falling sphere viscometry with X-ray radiography. The experiments were carried out in a 1500t multianvil apparatus at the SPring-8 synchrotron (Japan). A new, high-pressure sample assembly was developed with LaCrO₃ replacing the traditionally used graphite furnace material, allowing experiments within the diamond stability field to be carried out. The viscosity of CaMgSi₂O₆ liquid increases slightly from 3.5 to 10GPa and then decreases slightly at higher pressures. However, over the entire ranges of temperature (2030–2473K) and pressure (3.5–13GPa) investigated, variation in viscosity does not exceed ±0.5log units. The viscosity results from this study are consistent with those calculated from the pressure dependence of oxygen self-diffusion in CaMgSi₂O₆ liquid using the Eyring equation with a …