Local states of Fe (super 2+) and Mg (super 2+) in magnesium-rich olivines Available to Purchase

⁵⁷Fe Mössbauer spectra of a synthetic forsterite and of one natural olivine were studied at temperatures between 4.2 and 1223 K. Spectra were also taken at pressures between 1 and 30 kbar at 568 K and in external magnetic fields between 4 and 7 T at 295 K and 4.2 K. The signs of the electric field gradient at M1 and M2 are positive. The average value of the two asymmetry parameters η is 0.20±0.05. The force constants of Fe²⁺ at M1 and M2 are 4.7±0.1 eV/Ų and 4.2±0.1 eV/Ų, respectively. The axial splitting δ is 1120±50 cm^-1 for both sites. The comparison of the ⁵⁷Fe data with the previous ²⁵Mg data allows a more detailed analysis of total, lattice, and Fe²⁺ valence field gradients at the M1 and M2 sites. The observed apparent lack of site preference for Fe²⁺ can be interpreted in terms of the local electronic properties.