Corundum, rutile, periclase, and CaO in Ca,Al-rich inclusions from carbonaceous chondrites.

Four calcium,aluminum-rich inclusions from four carbonaceous chondrites-Allende, Acfer 082, Acfer 086, and Acfer 094-were studied by transmission electron microscopy. All inclusions contained at least two of the oxides periclase (MgO), rutile (TiO2), calcium oxide (CaO), and corundum (Al2O3). The oxides (50 to 200 nanometers in size) were found inside and at grain boundaries of the constituent minerals of the inclusions. Determining how these oxides formed may provide insight about condensation processes in the early solar nebula and the origin of refractory inclusions in chondrites. Formation of these oxides by exsolution is considered unlikely. An origin by kinetically controlled condensation appears more probable.