I am a little confused by page 16 of the GWB Reactive Transport Modelling Guide. It implies that swapping a mineral into the basis is equivalent to declaring equilibrium between that mineral and the solution being constructed. Why is this the case? Surely its possible to express the chemical composition of a solution in terms of a dissolved mineral (rather than its constituent ions, for example) without the solution actually being saturation with respect to that mineral.
Thanks in advance,
William
