The Role of Mg 2+ as an Impurity in Calcite Growth

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Abstract
Magnesium is a key determinant in CaCO 3 mineralization; however, macroscopic observations have failed to provide a clear physical understanding of how magnesium modifies carbonate growth. Atomic force microscopy was used to resolve the mechanism of calcite inhibition by magnesium through molecular-scale determination of the thermodynamic and kinetic controls of magnesium on calcite formation. Comparison of directly measured step velocities to standard impurity models demonstrated that enhanced mineral solubility through magnesium incorporation inhibited calcite growth. Terrace width measurements on calcite growth spirals were consistent with a decrease in effective supersaturation due to magnesium incorporation. Ca 1− x Mg x CO 3 solubilities determined from microscopic observations of step dynamics can thus be linked to macroscopic measurements.