Has the REE composition of seawater changed over geological time?

In this paper, we present a generalisation of the classical growth rate equations to the case of crystallisation in solid solution–aqueous solution solution (SS-AS) systems. In these new equations, basic growth parameters, interfacial free energy and supersaturation are functions of the solid composition. Therefore, each equation describes, for a given aqueous solution, a growth rate distribution as a function of the solid composition. Different crystal growth models such as two-dimensional nucleation or spiral growth mechanisms provide different growth rate distributions. We have studied the general behaviour of growth rate equations in solid solution–aqueous (SS-AS) systems. Finally, we have applied the generalised growth rate equations to the BaxSr1−xSO4–H2O SS-AS system. It allowed us to determine relationships between growth mechanisms and solid composition in such a model system. The result of our calculations were discussed and compared with previous experimental work on the BaxSr1−xSO4–H2O SS-AS system.