Physico-chemical modeling of the atmospheric-lithospheric interaction on Venus is presented. The thermodynamic assessment is carried out in terms of Venera 11 and 12 and Pioneer Venus measurements and the dynamic atmospheric structure. The subcloud atmosphere is interpreted to be a zone of nonequilibrium chemical conditions while the near-surface layer is presumed to be an equilibrium zone due to catalytic effects and low wind velocities. The mineral assemblages of the 'weathering crust' are calculated. The pyrite-anhydrite-magnetite assemblage is suggested as the buffering system resulting in reducing conditions (PO2≈10-21 atm). The existence of hydration is problematic and is thermodynamically conceivable only for the sulfur enrichment of primary rocks (about 2 wt.%). The carbonate minerals are suggested to be unstable.