Direct observations of mineral fluid reactions using atomic force microscopy: the specific example of calcite

Atomic force microscopy (AFM) enables in situ observations of mineral fluid reactions to be made at a nanoscale. During the past 20 years, the direct observation of mineral surfaces at molecular resolution during dissolution and growth has made significant contributions toward improvements in our understanding of the dynamics of mineral fluid reactions at the atomic scale. Observations and kinetic measurements of dissolution and growth from AFM experiments give valuable evidence for crystal dissolution and growth mechanisms, either confirming existing models or revealing their limitations. Modifications to theories can be made in the light of experimental evidence generated by AFM. Significant changes in the kinetics and mechanisms of crystallization and dissolution processes occur when the chemical and physical parameters of solutions, including the presence of impurity molecules or background electrolytes, are altered. Calcite has received considerable attention in AFM studies due to its central role in geochemical and biomineralization processes. This review summarizes the extensive literature on the dissolution and growth of calcite that has been generated by AFM studies, including the influence of fluid characteristics such as supersaturation, solution stoichiometry, pH, temperature and the presence of impurities.