Skin-Deep Surface Patterning of Calcite

The influence of soluble additives on the growth of calcite (CaCO3) is usually rationalized based on changes in crystal morphologies, where preferential association of the additives with either the acute or obtuse steps on the crystal surface gives rise to specific growth forms. In this work we investigate the influence of a highly acidic organic additive with calcite, cp20k from the barnacle Megabalanus rosa, and demonstrate that in addition to modifying the crystal morphology, additives can be used to generate calcite crystals with different surface architectures. These can potentially rise to interesting optical effects that may be important in applications such as in coatings and paints. These surface features form during dissolution/reprecipitation at the crystal surface during the incubation of crystals in solution, and confocal fluorescence microscopy confirmed they are limited to the surface of the crystal only. The surface patterning can also be tuned using alternative additives, mixtures of additives and by varying the solution conditions. Notably, we also show that surface structures can be used to determine the mode of interaction of additives with the microscopic surface steps under conditions where only minor changes in morphology have occurred.