Metallurgical coke, the primary fuel of the ironmaking blast furnace contains approximately 8-12% mineral matter and carbon. The formation and development of the mineral matter layer that formed between coke and liquid iron during carbon dissolution has been investigated. Coke particles (-2mm, +0.5mm) were added to the top surface of an iron 2 mass% C melt at representative ironmaking temperatures of 1450oC, 1500oC and 1550oC, for periods of time between 2 minutes and 120 minutes, before being quenched. The samples were then sectioned and the coke-iron interface examined in the SEM. The mineral matter layer that formed during the dissolution of carbon from coke into liquid iron has been found to form a solid layer of calcium aluminates at the coke-metal interface. The composition and morphology of these calcium aluminates was observed to change over time, changing from an open acicular structure to a dense structure. The change in the composition and morphology of these aluminates was also observed to have a significant role in determining the rate of the coke(carbon) dissolution. The changes observed in the rate can be directly attributed to the densification of the interfacial mineral layer impeding irons contact with the coke. In the ironmaking blast furnace this densification of a mineral matter layer will reduce the efficiency of the ironmaking process by prohibiting the dissolution of coke. By understanding this process ironmakers can optimise coke usage in the blast furnace, reducing coke consumption, operating costs and emissions of CO2.