Structure of the (10(1)over-bar4) surfaces of calcite, dolomite and magnesite under wet and dry conditions

Atomistic computer simulation methods have been employed to model the struc ture of the (10(1) over bar4) surfaces of calcite (CaCO3), dolomite [CaMg(C O3)(2)] and magnesite (MgCO3). Our calculations show that, under anhydrous vacuum conditions, calcite undergoes the greatest degree of surface relaxat ion with rotation and distortion of the carbonate group accompanied by move ment of the calcium ion. The magnesite surface is the least distorted of th e three carbonates, with dolomite being intermediate to the two end members . When water molecules are placed on the surface to produce complete monola yer coverage, the surfaces of all three carbonate minerals are stabilized a nd the amount of relaxation in the surface layers substantially reduced. Of the three phases, dolomite shows the strongest and highest number of inter facial hydrogen bonds between water and the carbonate mineral surface. Thes e calculations suggest that the equilibrium H2O + CO32- reversible arrow HC O3- + OH- will favour the production of hydrogen carbonate ions most strong ly for dolomite, less strongly for calcite, and least likely for magnesite.