Preliminary 57Fe Mössbauer study of metamict gadolinite REE2Fe2+Be2Si2O10 annealed at 1373 K in argon

Metamict minerals contain uranium and thorium, the decay of which results in the degradation of their crystal structures. This paper reports the preliminary study of 57Fe Mössbauer spectroscopy and X-ray diffraction analysis of metamict gadolinite REE2Fe2+Be2Si2O10 after isothermal annealing at 1373 K in argon. The Mössbauer spectra for samples annealed for 0.5, 3, 8, 15, and 60 min can be fitted to one Fe2+ quadrupole doublet with a strong asymmetry of the Fe2+ absorption peaks. Despite the almost instantaneous recrystallization at 1373 K, slight but noticeable changes in the amplitude and line width ratios of the absorption peaks and quadrupole splitting caused by extending the annealing time are observed. These changes in hyperfine parameters as a function of annealing time can be used to determine the activation energy of the isothermal recrystallization process.