dense than the average melt density (~2.67 g/cm 3 ) calculated for associated Mg-poor nephelinite liquids at the same conditions and volatile-free. However, the dissolution of 10.1 wt% H 2 O and 8.7 wt% CO 2 in the average nephelinite melt (based on volatile contents reported in the literature for these magmas) reduces its density to ~2.14 g/ cm 3 at 1150 °C and 1 GPa, eliminating the buoyancy contrast with the natrocarbonate melt. In turn, it is highly likely that the natrocarbonatite melts contained significant amounts of dissolved H 2 O and, as an example, the addition of 10 wt% H 2 O lowers the melt density by ~14 % to ~1.88 g/cm 3 , and therefore re-establishes a large density contrast with the volatile-rich nephelinite melts.