Structure of the (104) surfaces of calcite, dolomite and magnesite under wet and dry conditions

Abstract

Atomistic computer simulation methods have been employed to model the structure of the (104) surfaces of calcite (CaCO₃), dolomite [CaMg(CO₃)₂] and magnesite (MgCO₃). Our calculations show that, under anhydrous vacuum conditions, calcite undergoes the greatest degree of surface relaxation with rotation and distortion of the carbonate group accompanied by movement of the calcium ion. The magnesite surface is the least distorted of the three carbonates, with dolomite being intermediate to the two end members. When water molecules are placed on the surface to produce complete monolayer coverage, the surfaces of all three carbonate minerals are stabilized and the amount of relaxation in the surface layers substantially reduced. Of the three phases, dolomite shows the strongest and highest number of interfacial hydrogen bonds between water and the carbonate mineral surface. These calculations suggest that the equilibrium H₂O + CO₃²⁻⇌HCO₃⁻ + OH⁻ will favour the production of hydrogen carbonate ions most strongly for dolomite, less strongly for calcite, and least likely for magnesite.