Transmission 57Fe Mössbauer measurements were acquired in the temperature range 11–745 K from a suite of nine synthetic Ca-free P21/c Mg-Fe clinopyroxenes (cpx) along the MgSiO3-FeSiO3 join. The paramagnetic Mössbauer spectra (MS) consist of one doublet produced by Fe2+ ions at an almost regular octahedral M1 site and a second doublet at a more distorted octahedral M2 site. The temperature dependencies of the Fe2+ center shifts were fit to equations derived from the Debye model for the lattice vibrations, allowing the determination of the characteristic Mössbauer temperatures for the two Fe sites. The temperature variations of the M1 and M2 quadrupole splitting ΔEQ(T) are consistent with the higher distortions of the M2 octahedra. Applied-field MS revealed that the principal component of the electric field gradient, Vzz, is positive, implying a tetragonal compression of both octahedral sites. The crystal-field model was used to analyze ΔEQ(T) and to calculate the energy gaps Δ1 and Δ2 of the first excited electronic states within the 5D orbital term, both at M1 and M2. The various physical quantities derived from the MS are discussed in terms of the Fe/(Fe + Mg) ratio.

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