Epitaxy of Rhodochrosite (MnCO) on Muscovite Mica and Its Relation with Calcite (CaCO).

The flatness of muscovite mica makes it a convenient substrate to study epitaxy. We have analyzed the growth of rhodochrosite (MnCO) crystals in solution and on muscovite mica. Growth at high supersaturations occurs via the formation of amorphous MnCO, which over time transforms into the crystalline form. In the presence of muscovite mica, epitaxial rhodochrosite crystals with a size of approximately 1 μm form. These crystals are kinetically roughened, because of the high supersaturation. The lattice match between MnCO and muscovite was found not to be the main reason for epitaxy. If the growth experiment is performed twice, the original epitaxial MnCO crystals are overgrown by many small crystallites. Similarly, spherical MnCO crystals with many overgrown facets can be formed on a muscovite surface that is exposed to humidity or by using a higher MnCO supersaturation. A comparison with calcite shows that epitaxy strongly depends on initial supersaturation for both carbonates. In contrast to previous studies, we find that at the right supersaturation, epitaxial calcite crystal growth is possible on freshly cleaved muscovite.