ABSTRACT

The fine-grained white inclusions in the Allende meteorite have been studied by the scanning electron microscope with non-dispersive and dispersive X-ray detector, and a transmission electron microscope. The white inclusions consist almost entirely of the aggregates of losely packed semi-euhedral crystals rich in Ca and Al on the whole. Whisker crystals 0.5-5 microns in width and 10-50 microns long are found in cavities about 0.1 mm in diameter. These whisker crystals are wollastonite (CaSiO₃) whose formation process has not been fully elucidated with the equilibrium condensation. On the basis of the evidence that a portion of the wall of the wollastonite-filled cavity is rich in Al₂O₃, we presumed some possible formation processes of these wollastonite whiskers. In conjunction with a finding of layered rims enclosing Ca-Al rich inclusions in carbonaceous chondrites, the growth of wollastonite whiskers in the inclusions also provide an evidence that some post-condensation processes took place within the inclusions as well as at the rims.