Preferential occupation of pyroxene sites by iron in diogenite meteorites

Three diogenite meteorites ALHA77256-121, Tatahounie and Bilanga are studied using Mossbauer spectroscopy to look at the iron occupancy in the two inequivalent pyroxene sites. Though the three meteorites belong to three different conditions, one is an Antarctica find, one is 75 years old fall and one is a recent fall, the iron occupancy in pyroxene sites is very similar. Fe2+ occupies only the less distorted site and hence a single sharp doublet is observed in the Mossbauer spectra of all these samples. In contrast eucrites show a distribution of iron ions in the two sites of pyroxenes.