Crust and mantle processes yield mineral assemblages which are not generally stable in Earth surface environments. Uplift to the zone of weathering therefore initiates chemical reactions which produce quite different assemblages. The precise nature of the resulting minerals depends much upon the composition of the aqueous phase present. Erosion, sedimentation and diagenesis move weathering products through a succession of chemical environments. Further solid-solution reactions occur at each stage. Until recently, the least-well documented part of this cycle was burial diagenesis. New information provided by oil companies from their submarine exploration programmes has done much to rectify the situation. It is now possible to present a fairly complete account of the important chemical reactions occurring at each stage of the surface cycle. The major conclusion to be drawn from this exercise is that reactions involving an aqueous phase play a very important part in geological evolution as a whole.