It is well known that oxide glasses build up continuous networks. Therefore the rigidity of the latter plays a key role in understanding glass properties. The network switches from floppy to rigid if the number of covalent bridges between the network formers exceeds a certain threshold value. One and the same structure could have behave as rigid network in respect to some properties and could be floppy networks in respect to some other properties. Kinetics of phase transition (and most the nucleation processes) is very sensitive to the rigidity of the network. Some tiny floppy regions still exist inside the rigid network close above the threshold concentration. They can serve as active centres for the beginning of the nucleation process. Much later, nucleation can appear in the rigid part of the network. Therefore, we predict a certain interval of concentration of rigid bounds in which a bimodal size distribution function of the formed phase will be observed. This prediction is confirmed by experimental data we find in literature.
