Stability of ilmenite and titanomagnetite in the presence of carbon dioxide — A thermodynamic evaluation

The stability of ilmenite and titanomagnetite in the presence of CO₂ gas was evaluated thermodynamically. Ilmenite with a composition Ilm₉₀Hm₁₀ breaks down to the assemblage siderite-hematite-anatase below 270° C at 1,000 bars and below 300° C at 2,000 bars. Titanomagnetite with a composition Usp₅₀Mt₅₀ breaks down to the same assemblage below 345° C at 1,000 bars and below 385° C at 2,000 bars. During the low-grade metamorphism of basaltic rocks, a CO₂ partial pressure of only a few hundreds bars is sufficient to alter ilmenite and titanomagnetite to the assemblage siderite-hematite-anatase.