The Use of Selected-Area Electron Diffraction in Meteorite Mineralogy

Abstract

The use of precision goniometer stages on electron microscopes for study of mineral constituents of carbonaceous meteorites is discussed. Results to date have identified olivine positively in a Type I meteorite and indicated a range of composition for olivine in Type II meteorites in agreement with earlier work. Compositional variations are observed among layer lattice silicates from both types and in spinels from Type I. Structural disorder noted in pyroxene and in stacking of layers in layer lattice silicate is believed to be a growth effect, although subsequent shock cannot be ruled out now. Results support the hypothesis that carbonaceous meteorites are mechanical mixtures of minerals, little altered since formation. Mild hydrothermal action is noted on a few minerals.