This study has quantified the amount of silica vaporised during the combustion of five Australian bituminous coals in a drop tube furnace at two oxygen partial pressures. The coals have been analysed extensively using a wide range of analytical techniques including QEMSCAN, quantitative XRD analysis, and ICP-AES. These analyses provided the modes of occurrence of the silica in these coals. The amounts vaporised were compared with the modes of occurrence of the silica, to determine the factors contributing to its vaporisation. Three main conclusions were drawn from these experiments:•Increasing the char combustion temperature by elevating the oxygen partial pressure from 0.21 to 0.50 atm during combustion increases the extent of silica vaporisation significantly. This is consistent with previous findings.•The size distribution of the included quartz minerals greater than 2 μm does not affect the extent of silica vaporisation significantly,•Qualitative measurements indicate that finely dispersed silicon-bearing minerals of a size less than 2 μm could play an important role on the vaporisation of silica. An analytical procedure to quantify these minerals is necessary to establish this relationship.