The optical absorption spectra of Fe2+ in the M(2) site of orthopyroxene have been reanalyzed, in view of the experimental observation of a mid-infrared band at 2350 cm−1 arising from an electronic transition within the split 5T2g ground state of the low-symmetry site. This analysis uses C2v spectroscopic symmetry and a crystal-field potential which includes fourth-order harmonic terms. The order of the energy states is found to depend upon specific bond angles and lengths. The 2350 cm−1 band is assigned as a transition to the 5B2 state, calculated to lie above the 5A2 state. This result indicates that the entire splitting of the 6T2g ground state is 2350 cm−1.

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