Epitaxies of Ca-sulfates on calcite (CaCO3) I. Gypsum {010} on the calcite {10.4} form: epi-twins of gypsum induced by the calcite substrate

3D-epitaxy of the {010} pinacoid of deposited gypsum (CaSO4 center dot 2H(2)O) on the substrate {10.4} calcite rhombohedron is described, in order to give a theoretical background to the replacement of calcite with gypsum both in the laboratory and by weathering in nature. 2D-lattice coincidences are geometrically obtained from the matching of periodic bond chains (PBCs) running within the elementary slices facing towards the substrate/deposit interfaces. The epitaxy in the third dimension, perpendicular to the interfaces, has been verified as well, to establish if ad/absorption occurs (anomalous mixed crystals) at the calcite/gypsum contact. This research represents the reticular part of a wider program extended to the epi-interaction among the gypsum/calcite, gypsum/bassanite (CaSO4 center dot 1/2H(2)O) and gypsum/anhydrite (CaSO4) couples.

Automated summary

This study describes the 3D epitaxy of deposited gypsum on calcite substrates, providing a theoretical background for the replacement of calcite by gypsum in both laboratory and natural weathering conditions. 2D lattice coincidences are obtained from the matching of periodic bond chains running within the interfaces. The study also investigates the absorption and adsorption at the calcite/gypsum contact in the third dimension. This research is part of a broader program on the epi-interactions among gypsum/calcite, gypsum/bassanite, and gypsum/anhydrite couples.