Mapping magnesites: carbon mineralization processes yield MgCO3 with highly variable morphology and thermodynamic stabilities

• Parameters of carbon mineralization routes greatly affect magnesite properties. • Magnesite’s distinct properties relate to variable thermodynamic stabilities. • The relationship between production route and physico-chemical properties revealed. • Awareness of magnesite’s differences improve utilization prospects. Carbon capture and utilization via mineralization (CCUM) is the most promising pathway for scalable mitigation of anthropogenic emissions. MgO-rich feedstocks are particularly promising: they are globally abundant and have potential applications in construction materials, which could enable permanent storage of up to 16 Gt CO 2 annually. Crucial to their performance is the formation of anhydrous magnesium carbonate (magnesite, MgCO 3 ), a thermodynamically stable phase with high CO 2 -storing capacity. In the current work, seven types of magnesite, produced via three CCUM routes, were characterized by SEM, XRD, TGA, BET, FTIR, Raman, and luminescence spectroscopy. We demonstrate that, by choosing the CCUM route, one can tune magnesite’s properties to a great degree: the most vs. least reactive magnesite, having highest vs. lowest solubility, had values of crystallite size (319 vs. 725 nm), BET (16.8 vs. 0.3 m 2 /g), TGA decarbonation occurrence (500 vs. 670 °C), skeletal density (2.8 vs. 3.1 g/cm 3 ), and log K sp @80 °C (−8 vs. −9.4 mmol 2 /L 2 ), indicating potential as cementitious materials for the most reactive or fillers for the least reactive magnesite in cement.