Abstract
Gadolinite, REE2FeBe2Si2O10, is commonly metamict. 57Fe Mössbauer annealing studies of fully metamict gadolinite from Ytterby, Sweden, have been completed in argon atmosphere from 873 to 1473 K. This technique has rarely been employed in studies of metamict minerals. Changes in the experimental parameters of Mössbauer spectra are sensitive indicators of the thermal recrystallization process of metamict gadolinite and revealed two stages of the structural recovery: a major stage from 873 to 1073 K and a slower recovery stage from 1133 to 1473 K. These observations are confirmed by X-ray powder diffraction. In relation to the first stage, the exponential behaviour of the changes in the Mössbauer parameters can be used for deriving the activation energy E a of the recrystallization process. The calculated value E a =1.97 eV in argon atmosphere explains the common occurrence of gadolinite in the fully or partially metamict state. Results of Mössbauer spectroscopy suggest that the recrystallization of metamict gadolinite is a displacive transition that involves rotation and translation of SiO4 and BeO4 to their normal positions associated with removal of OH groups from the structure.
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Received: 30 April 2001 / Accepted: 28 September 2001
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Malczewski, D., Janeczek, J. Activation energy of annealed metamict gadolinite from 57Fe Mössbauer spectroscopy. Phys Chem Min 29, 226–232 (2002). https://doi.org/10.1007/s00269-001-0221-7
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DOI: https://doi.org/10.1007/s00269-001-0221-7