STEP DYNAMICS AND SPIRAL GROWTH ON CALCITE

We present novel in situ observations of the dynamics of monomolecular growth steps on calcite. Steps do not interact at separations of approximately 10 nm and above, indicating that surface diffusion does not control calcite growth. Instead, steps advance by material addition from solution onto step sites or a narrow adjacent zone. Step nucleation is primarily at growth spirals, and no spontaneous surface nucleation is observed; growth rate is controlled by spiral rotation rate. Thus, classical growth models based on rapid surface diffusion are inapplicable to calcite and possibly to many other minerals.