Druse Pyroxenes in D’Orbigny: A Mössbauer Spectroscopy Study

D’Orbigny meteorite, the largest angrite known, is peculiar in its abundance of hollow shells, abundant presence of glasses, and open druses with perfectly crystallized augites of prismatic habit. We report on the distribution of Fe2+ among the nonequivalent sites in the druse pyroxenes of D’Orbigny using Mossbauer spectroscopy measurements on 200 mg of euhedral augites (70–400 mm). Electron microprobe analyses showed augites chemically homogeneous with a slight compositional change at the outermost ∼5 μ (rim). Cation distribution over nonequivalent lattice sites in minerals can give information on its pT history. When pyroxene crystals cool slowly to temperatures below 500°C, the Fe2+ ions populate primarily the M2 position, whereas the Mg2+ ions occupy predominantly the M1 position. Crystals cooling rapidly have a more disordered Mg,Fe distribution over the M1 sites. Mossbauer spectra of our sample obtained at RT consist of an intense inner doublet due to Fe2+ at the M2 sites and a less intense outer do...