A micro-macro chemo-mechanical model of damage and healing is proposed to predict the evolution of salt stiffness and deformation upon micro-crack propagation, opening, closure and rebonding, which is the result of pressure solution. We hypothesize that at a given grain contact, the surface area of contact dictates which mechanism dominates the rate of chemical process. Based on thermodynamic equations of dissolution, diffusion and precipitation, we establish a formula for the critical contact area that marks the transition between diffusion-dominated kinetics and dissolution-precipitation-dominated kinetics. We relate the change of contact area to the change of solid volume in the Representative Elementary Volume, and we define net damage as the sum of the mechanical damage and the chemical porosity change. A continuum-based damage mechanics framework is used to deduce the change of salt stiffness with net damage. A stress path comprising a tensile loading, a compressive unloading, a creep-chemical stage and a reloading is simulated. Stiffness degradation and residual strain development are observed with the evolution of damage under tensile loading. Unilateral effects of crack closure can be predicted by the model upon compression. Our micro-macro model also allows predicting the evolution of the probability distribution of contact areas upon chemical effects, as well as the consequent change of net damage and stiffness. The proposed modeling framework is expected to shed light on coupled chemical processes that govern microstructure changes and subsequent variations of deformation rate, stiffness and permeability in salt rock, and to allow the assessment of long-term behavior of geological storage facilities in salt.