The influence of Ca-Mg disorder on the growth of dolomite. A computational study
We performed empirical calculations at 0K on (10.4) slabs of dolomite with increasing thickness and different Ca2+-Mg2+ distributions (i.e., different degree of structural disorder) in the 10.4 layers forming the slab. The energy of isolated (10.4) dolomite slabs and (10.4) dolomite slabs in epitaxy with (10.4) calcite slabs, was determined. In particular, the (i) average potential energy, (ii) specific adhesion energy and (iii) excess free energy due to the presence of the interfaces, were calculated for all the systems investigated. These data allowed us to propose a new growth model for primary dolomite, which hypothesizes that dolomite forms from a Ca2+-Mg2+-rich fluid by nucleating initially small calcite crystals, which act as substrates for successive dolomite formation. Moreover, our calculations suggest that the dolomite layers forming at the dolomite/calcite and dolomite/solution interfaces are disordered for increasing the adhesion energy and decreasing the surface energy. Then, a disordered dolomite/calcite interface seems to promote dolomite growth.