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 1250–1325°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.