| Abstract: | Site occupancy numbers for ferrous iron, magnesium, and calcium at the Ml and M2 sites in lunar clinopyroxenes are estimated from nuclear gamma-ray resonant absorption spectra of (57)Fe. The cation distribution is ordered; calcium and magnesium prefer M2 and Ml, respectively. The distribution corresponds to an equilibrium at a temperature lower than 680 degrees C. Crystals cleaved and sectioned by diamond-knife ultramicrotomy were examined by high-voltage (200 kv) electron microscopy and diffraction. Uniform 300-to 600-A-wide bands that correspond to single crystal domains were found. Correlation of the bands with magnetic ordering at low temperatures is considered. |
