Structure–Composition Relationships in the Dolomite–Ankerite–Kutnohorite Series Reveal Distinctions Based on Growth Conditions and Cation Ordering

Carbonate minerals are important carbon sinks that have acted to regulate Earth’s climate throughout geologic history. Developing the ability to accelerate their formation is a promising approach to help mitigate global climate disruption from anthropogenic CO2 emissions. Here we compiled and analyzed a diffraction database to examine relationships between the structures and compositions of natural and synthetic double carbonates from the dolomite–ankerite–kutnohorite series. Data was carefully curated from both the International Centre for Diffraction Data powder diffraction file database and the broad literature, whereby lattice spacings, cell parameters and volumes were plotted against composition. Theoretical structures generated using density functional theory (DFT) energy minimizations were used to assess the impact of cation ordering on cell parameters. The collective findings reveal structural distinctions between natural and synthetic samples likely arising from the extent of cation ordering, a characteristic promoted during slow growth of natural samples versus the relatively fast growth of synthetic samples. They also highlight structural parameters that can be used as a basis to predict composition, and vice versa. The insights help advance a fundamental understanding of double carbonate minerals common in nature that also comprise compelling targets for accelerated carbon mineralization.