In this study, the mineral matter layer that forms between coke, and liquid iron during carbon dissolution has been characterised. Rectangular prisms of coke were immersed in an iron–2 mass% carbon melt at representative ironmaking temperatures for 20 min then drop quenched. The quench sample was then sectioned and the coke–iron interface was examined in the SEM. A mineral matter layer was observed at the experimental temperatures 1 400°C, 1 450°C and 1 500°C, but not at 1 550°C. Though no layer was found at 1 550°C a slag was observed on the metal surface. This slag was not evident at other temperatures. The formation of the mineral matter layer and its temperature dependence is described in terms of a temperature activated fusion process. Further the mineral matter layer and adjacent coke were found to be significantly depleted in SiO2. This has been explained in terms of SiO2 reduction.