The destruction of the crystalline order via external mechanical effects, e.g. by intensive grinding, is an important phenomenon of mechanochemistry and is denominated by the author as "structural activation". The mechanochemical structural activation is actually a result of two opposite processes: one is the destruction of the crystalline structure (amorphisation, AM), the other is a densification in the microenvironment within the grains or between the amorphous grains and also a certain degree recombination. The dynamic balance of the two processes results in the final state of the milling product, which can be assessed by the measurement of oxygen density. The mechanochemical balance can be interpreted as the destruction of the structure of crystalline materials and is immediately followed by partial densification of high free energy amorphous atomic aggregates to a more stable and denser, although still amorphous, product. The dominance of recombination processes of the originally amorphous materials on prolonged milling is demonstrated.