SFCA (silico ferrite of calcium and aluminium), SFCA-I and now SFCA-III are well-known iron ore sinter bonding matrix phases. SFCA (n = 0), SFCA-I (n =1) and SFCA-III (n = 2) form a polysomatic series with general formula M14+6nO20+8n. Each structure consists of distinct ordering of spinel (S) and pyroxene (P) modules; SPSPSP for SFCA, SSPSSP for SFCA-I, and SSSPSSSP for SFCA-III. The SFCA-III phase, which has only been identified and described relatively recently, has general formula M26O36 – for example, Ca2.99Al4.56Fe15.35Si0.43Mg2.67O36 – and triclinic crystal structure (Kahlenberg, Krüger and Goettgens, 2019). Zöll et al (2018) reported investigations into FCAM-III which has similar structure to SFCA-III but in the SiO2-free system. SFCA-III can be a significant component of industrial and pot-grate iron ore sinter (Webster and Pownceby, 2024; Clout et al, 2026), and more detailed and extensive fundamental knowledge about its compositional limits and crystal chemistry is important for the field of iron ore sintering research and characterisation.