Carbonatites are rare but worldwide occurring igneous rocks and their genesis remains enigmatic. Field studies show a close spatial but controversially debated genetic relationship with alkaline silicate rocks, and petrological and experimental studies indicate liquid immiscibility from mantle-derived magmas being one viable model for the generation of carbonatites. However, unaltered carbonatitic melts are rare and the composition of primary carbonate liquids and their silicate conjugates is poorly constrained. Here we show an example of primary Ca-carbonatitic melt formed by liquid immiscibility from a phonolitic magma of the Laacher See volcano (Eifel, Germany). The conjugate blebs of carbonate-silicate liquids are found in hauyne-hosted melt inclusions. The Ca-carbonatite melts are moderately alkali-rich and contain high F and Cl at elevated SiO₂ and Al₂O₃ concentrations. Such carbonatite liquids are viable parental magmas to the globally dominating intrusive Ca-carbonatite complexes and may provide the missing link to extrusive Na-carbonatitic magmas.

Experimental measurements of density by X‐ray absorption and of P‐wave velocity by ultrasonic techniques of liquid Fe‐(<17 wt%) Si‐(<4.5 wt%) C alloys at pressures up to 5.8 GPa are presented. These data are used to construct an Fe‐Si‐C liquid mixing model and to characterize interior structure models of Mercury with liquid outer core composed of Fe‐Si‐C. The interior structure models are constrained by geodetic measurements of the planet, such as the obliquity and libration of Mercury. The results indicate that S and/or C with concentrations at the wt% level are likely required in Mercury's core to ensure the existence of an inner core with a radius (below ∼1,200 km) that is consistent with reported dynamo simulations for Mercury's magnetic field. Interior structure models with more than 14 wt% Si in the core, estimated for Mercury by assuming an EH chondrite‐like bulk composition, are only feasible if the obliquity of Mercury is near the upper limit of observational uncertainties (2.12 arcmin) and the mantle is dense (3.43–3.68 g·cm⁻³). Interior structure models with the central obliquity value (2.04 arcmin) and less than 7.5 wt% Si in the core, consistent with estimates of Mercury's core composition from an assumed CB chondrite‐like bulk composition, are compatible with 3.15–3.35 g·cm⁻³ mantle densities and an inner core radius below 1,200 km. Interior structure models with the obliquity of Mercury near the lower observational uncertainty limit (1.96 arcmin) have a low‐density mantle (2.88–3.03 g·cm⁻³), less than 4 wt% Si in the core, and an inner core radius larger than 1,600 km.

The use of silicate calibrants for ns LA-ICP-MS analyses of Fe-based samples results in significant matrix effects. The magnitude of these effects, defined by the fractionation index or F _i , is a function of elemental volatility. Using the dependency of the F _i with elemental volatility a predictive model was developed to correct for these effects.