Iron-wollastonites from skarns have an approximate composition of Ca₅FeSi₆-O₁₈. Iron-wollastonites and ordinary wollastonites from the Kagata mine are associated with clinopyroxenes of hedenbergite and ferrosalite compositions, respectively. This fact could be interpreted as that a miscibility gap exists between iron-wollastonite of Ca₅FeSi₆-O₁₈ composition and ordinary wollastonite. Thus iron-wollastonite of Ca₅FeSi₆-O₁₈ composition appears to be a stable phase in the CaSiO₃-CaFeSi₂O₆ join at temperatures as low as those of the skarn formation, probably 300°∼600°C.