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Metamictization and recrystallization of titanite: An infrared spectroscopic study

¹ Department of Earth Sciences, University of Cambridge, Downing Street, Cambridge, CB2 3EQ, U.K.
² Mineralogisch-Petrographisches Institut, Universität Hamburg, Grindelallee 48, D-20146 Hamburg, Germany
³ Department of Earth and Ocean Sciences, University of British Columbia Vancouver, British Columbia, V6T 1Z4, Canada
⁴ Institut für Mineralogie, Westfälische Wilhelms-Universität Münster Corrensstr. 24, D-48149 Münster, Germany

Correspondence: ^* E-mail: mz10001{at}esc.cam.ac.uk

Radiation damage and the recrystallization of natural titanite (CaTiSiO₅) were studied using infrared spectroscopy in the spectral range from 50 to 7500 cm^–1. The results show that radiation damage leads to systematic changes in spectral features: decreasing absorption and reflectivity, line broadening, and loss of orientational dependence. Strongly damaged titanite shows hydroxylate bands between 2200 and 3500 cm^–1. The band most affected by radiation damage is the Ti-O stretching band near 670 cm^–1. It shifts to 710 cm^–1 in the most damaged samples, possibly indicating the presence of TiO₅ complexes in metamict titanite. Titanite glasses (quenched melts of CaTiSiO₅) show spectral features different from those of radiation-damaged titanite, especially in the Ti-O and Si-O stretching regions.

Annealing radiation-damaged titanites at high temperatures results in the recovery of damaged crystalline regions. Recrystallization near 900 K is characterized by an increase in reflectivity, integrated absorbance, and line sharpening. Different infrared bands show recovery at different temperatures. The restoration of the Ti-O stretching band near 670 cm^–1 and an infrared band near 285 cm^–1 took place at temperatures of 1200–1400 K. Temperature-induced changes of the OH-absorption bands could be responsible for the previously reported differences in the temperature evolution of infrared spectra of OH species between in situ and quench experiments.