Iron mass fraction of pebbles in the disc around the Sun as a function of disc viscosity and pebble fragmentation velocity. Purple dashed lines mark the location of the evaporation fronts of the various chemical species included in our model. Grey bands represent the range of values for the iron abundance of Mercury (Brugger et al. 2018; Adibekyan et al. 2021). Increasing the disc’s viscosity results in a lower pebble iron mass fraction because the rapid inflow of gas from the outer disc continuously transports freshly produced iron vapour away.