Study of the temperature dependence of the hyperfine parameters in two orthopyroxenes by 57Fe Mössbauer spectroscopy

⁵⁷Fe Mössbauer measurements were performed on two natural orthopyroxenes in the temperature range between 17 and 490 K. The temperature variations of the center shifts and of the quadrupole splittings have been interpreted using the Debye model for the lattice vibrations and the crystal-field model respectively. Two approaches have been applied to evaluate the crystal field. The first one, which is commonly used by Mössbauer spectroscopists, emanates from the approximative and simplified symmetry of the ferrous sites, whereas the second one takes into account the real C ₁ symmetry of the ferrous sites, thus leading to a pointcharge calculation. For comparison, analogous calculations have been carried out on literature data for an iron-rich orthopyroxene (specimen XYZ).Industrial Highschool BME, Voskenslaan, B-9000, Gent, Belgium