This study investigates spurrite (Ca 5 (SiO 4 ) 2 CO 3 ) formation under CO 2 -rich atmospheres relevant to oxyfuel combustion in cement kilns. Synthetic raw meals doped with 1.0–3.0 wt.% chloride were thermally treated at 800, 850, and 900 °C under air, 63 vol.% CO 2 , oxyfuel 1st gen., and pure oxyfuel conditions. Phase assemblages were analyzed by X-ray diffraction with Rietveld refinement and supported by thermodynamic modeling and a Design of Experiments approach. The results show that spurrite formation is strongly governed by the CO 2 partial pressure, with negligible formation under air and a pronounced increase under CO 2 -rich atmospheres. Maximum spurrite contents of up to 40 wt.% were observed at 900 °C. At high CO 2 concentrations, the increase in spurrite formation levels off, indicating a plateau effect. These findings highlight the dominant role of the gas atmosphere in spurrite stabilization and provide important insights into build-up risks in oxyfuel-driven cement kilns, supporting the implementation of carbon capture technologies. • Spurrite formation strongly increases with CO 2 partial pressure. • Temperature and CO 2 concentration govern spurrite content. • Holding time and chlorine concentration play minor roles on spurrite evolution. • Enhanced spurrite formation may pose a risk of deposit formation in future oxyfuel cement plants.