Silico-ferrites of calcium and aluminium (SFCA) are desirable phases in a high quality iron ore sinter product. The effects of sintering temperature, CaO/SiO2 ratio, sintering gas atmosphere and cooling procedure on the phase composition of sintered specimens from an industrial sinter blend were examined with focus on the formation of SFCA phases. The proportions of mineral phases in specimens sintered at 1 250-1 325°C were quantitatively examined using image analysis. SFCA can be formed at low temperatures by solid state reactions, the formation of which was enhanced by increasing temperature. Further increasing sintering temperature promoted the reduction of Fe3+ in the SFCA crystal structure to Fe2+ and consequent decomposition of SFCA. At high temperatures, SFCA was produced during cooling via crystallisation from a silicate melt. Maintaining a high oxygen partial pressure favours the formation of SFCA, either via solid state reactions or from a melt. This is attributed to hematite being available as a reactant for SFCA formation. Similarly, increasing CaO/SiO2 ratio provides more CaO as a reactant and promotes SFCA formation.