Hydrons species in crystalline and metamict titanites

The content of hydrous species in crystalline and metamict titanite (CaTiSi O5) have been investigated using polarized infrared spectroscopy. The effec ts of metamictization are a decrease of intensity and a broadening of Ti-O and Si-O stretching overtones, accompanied by development of the isotropic spectral features of hydrous species. Metamict and partially metamict titan ites show OH contents up to 0.73 wt% H2O on the basis of previously reporte d calibrations. On heating, crystalline and metamict titanite showed a diff erent temperature evolution of their OH content. Thermal annealing of cryst alline titanite at temperatures above 1100 K for 15 min resulted in dehydra tion, characterized by a dramatic decrease in the intensity of the OH signa l near 3486 cm(-1), in contrast to a two-stage dehydration process in metam ict titanite. The results show that the high OH contents in metamict titani tes are probably due to hydrogen diffusion during and after metamictzation. The results also show that the recrystallization in metamict titanite at h igh temperatures involves epitaxial growth of crystalline domains.