The system CaO–chromium oxide in air is reinvestigated and the existence of intermediate phases with chromium in oxidation states>3+ (Ca5Cr3O12, Ca3(CrO4)2, and Ca5(CrO4)3) confirmed. Under reducing conditions these phases are unstable. A metastable, polymorphic form of calcium chromite,δ‐CaCr2O4, is observed. In the CaO‐rich section of the CaO–Al2O3–Cr2O3system a ternary intermediate phase, chrome‐haüyne, Ca4[(Al,Cr3+)6O12](Cr6+O4), coexists with calcium chromate and calcium aluminate phases. In air, low melting temperatures are preserved in all assemblages containing calcium chromate phases. Under reducing conditions a new ternary phase, Ca6Al4Cr2O15, coexists with CaO, CaCr2O4, chrome‐haüyne, and calcium aluminate phases. The influence of chromium oxide additions on the solidus temperatures of the CaO–Al2O3syste