Figure 3

Energies for Mg ²⁺ substitution at Ca ²⁺ in aragonite surface sites. The substitution energies are shown as a function of the depth from the interface of (a) {001} and (b) {110} surfaces. Red lines are drawn at 93.1 kJ/mol, which is the energy for Mg²⁺ substitution into bulk aragonite. Layer numbers, [A], [A′], [A″], [B], [B′], and [B″] correspond to the substitution energies for the site shown in Figure 1.