Mössbauer Spectroscopy of Metamict Allanite From Ytterby (Sweden) Annealed at 973, 1073, and 1173 K in Argon

Abstract

The effect of annealing at temperatures of 973, 1073, and 1173 K on fully metamict allanite-(Ce), (Ce,Ca,REE)₂(Fe²⁺,Fe³⁺)(Al,Fe³⁺)₂O[Si₂O₇][SiO₄](OH) was studied using Mössbauer spectroscopy and powder X-ray diffraction. The Mössbauer spectra of the untreated sample and the samples annealed at 973, 1073, and 1173 K can be fitted to three Fe²⁺ doublets and one Fe³⁺ doublet. The relative contribution of ∑ Fe²⁺/∑ Fe in the Mössbauer spectra increases from 0.72 for the untreated  sample  to  0.86  for  the  sample  annealed  at  1173 K. The X-ray diffraction pattern of the fragment annealed at 1173 K indicates that the fully metamict allanite-(Ce) recrystallized into an apatite-like phase, and not into the crystalline phase of this mineral.