The occurrence of intermediate amorphous nanophases in the pure and mixed metal systems, followed by their restructuring and densification, demonstrated a multi-step crystallization route. Therefore, the TMPs crystallization is non-classical. Although the amorphous intermediate phases formed quickly in the early reaction stages, their reconfiguration and aggregation occurred gradually over many seconds to minutes. After a threshold density and µm-size of the agglomerates were reached, the final transformation to a crystal seemed to be very fast. Since the actual transformation to a crystalline material occured within seconds and exhibited highly stochastic characteristics, it proved challenging to be tracked with ex-situ approaches. Namely, transitional amorphous phases and final crystals can coexist within a limited metastable time window. Interestingly, neither individual nanocrystals nor standalone spherical building units were found in the samples. Instead, we observed only larger mesoscopic agglomerates of building units, or already crystals of µm-size. This suggests that the outcome of TMPs crystallization should be potentially controllable by confinement/finite volume . We speculate that the occurrence and the stability of the amorphous phases is actually controlled by meta-stable, but long-living aqua ammonia complexes (M 2+ (H2O)x(NH3)1-x) present in solutions, whose evolution affects the equilibria of the evolving solids . They may have an impact on crystallization i.e. on the formation of nm-sized clusters by decreasing the amount of available free Ni 2+ , Co 2+ or NH4 + ions. Such speciationdependent, solid vs. aqueous cluster equilibria would explain very different transformation kinetics of the amorphous phase agglomerates, including the anomalous evolution in the mixed-metal systems. Another kinetic reason to consider, in the light of the evolution of pH trends, are associated stabilities of different protonated phosphate species. Starting pH ≈ 8, such conditions would stabilize predominantly the single protonated HPO4 2-species while at the end of precipitation the drop in pH to 4.6 would shift the equilibrium to the double protonated H2PO4 -. The presence of different protonated phosphate ligands in an aqueous solution could potentially affect the local structure of strongly hydrated amorphous transition metal phosphate nanophases -analogously observed in calcium-carbonate and -phosphate systems . They could form similar frameworks as observed structures of Posner clusters in the crystallization pathway of apatite .