An experimental study characterising mineral layer formation at the coke-iron boundary during coke dissolution has been carried out. In this experimental study coke was added to the surface of an iron-carbon melt. Experiments were carried out at temperatures between 1450 and 1550°C for periods of time between 2 minutes and 120 minutes, before being quenched. Quenched samples were then sectioned and the solidified coke-melt interfacial region prepared for SEM and EDS analysis. SEM images and EDS analysis of the coke-iron interface revealed a mineral layer was present at the interface at all experimental temperatures and times. Further, it was determined that the layer was calcium aluminate based and that over time became progressively enriched with calcium. The predominant mineral layer was found to be composed of alumina, CA6, CA2 and CA phases, with the proportions of these phases dictating its morphology. At short experimental times the layer was predominantly alumina plus CA6 or CA6 plus CA2 with an open low density structure. At longer times the layer was predominantly CA2 plus CA with a dense structure. The change in morphology of the layer had a profound effect on the rate of the rate of carbon dissolution from the coke. The effect of this mineral layer on the rate of carbon dissolution has been interpreted as a change in the reaction control mechanism.