Epitactic Overgrowths of Calcite (CaCO3) on Anhydrite (CaSO4) Cleavage Surfaces

We investigate the crystallographic relationships between calcite crystals overgrown on the three main anhydrite cleavage surfaces, (100), (010), and (001), as a result of the interaction between anhydrite surfaces with carbonate-rich aqueous solutions (0.5 mol/L Na2CO3). Scanning electron microscope (SEM) images and energy back scattered diffraction (EBSD) analyses reveal that this interaction always leads to oriented nucleation and growth of calcite crystals, characterized by a parallelism between the calcite {1014} faces and the corresponding anhydrite cleavage surface. A high density of oriented calcite crystals was observed on the (001)Anh face, while the calcite crystal density was significantly lower on the (100)Anh and (010)Anh faces. On all investigated anhydrite cleavage surfaces, calcite {1014} showed at least two excellent matching orientations, both defined by the parallelism between ⟨441⟩Cal and one of the three crystallographic axes of anhydrite. As a result, two different populations of...