Abstract: Information about the behavior of silicate groups during metamictization of zircon is important for a full understanding of the structure of metamict state as well as the mechanism of the process of metamictization of this mineral. Although there is speculation that the creation of 0 vacancies may lead to a progressive polymerization of SiO₄ tetrahedra^[7], no direct experimental evidence supports it up to date. The ²⁹Si MAS NMR results of the present work show that no significant changes in the local structural environment of Si occur at the initial stage of mctamictization. However, Q³ and Q⁴ Si environments were detected in zircons with mediate degree of metamictization (DOM), indicating that the intrease of DOM leads to a polymerization of SiO₄ tetrahedra. The products of polymerization must be amorphous because no crystalline phases other than zircon were detected by XRD. The results of infrared measurments also indicate that domains of amorphous silica may exist in metamict zircons.

Key words: Zircon, Metamictization, ²⁹Si MAS NMR spectroscopy, Infrared spectroscopy