Condensation and aggregation of solar corundum and corundum-hibonite grains

T. M. Nakamura, N. Sugiura, M. Kimura, A. Miyazaki, A. N. Krot

Research output: Contribution to journalArticlepeer-review

14 Citations (Scopus)


Forty-three corundum grains (1-11 μm in size) and 5 corundum-hibonite grains with corundum overgrown by hibonite (4-7 μm in size), were found in the matrix of the mineralogically pristine, ungrouped carbonaceous chondrite Acfer 094 by using cathodoluminescence imaging. Some of the corundum and corundum-hibonite grains occur as aggregates of 2 to 6 grains having similar sizes. The oxygen isotopic compositions of some of the corundum-bearing grains suggest their solar nebula origin. 26Al-26Mg systematics of one corundum grain showed the canonical initial 26Al/27Al ratio, also suggesting a solar nebula origin. Quantitative evaluation of condensation and accretion processes made based on the homogeneous nucleation of corundum, diffusion-controlled hibonite formation, collisions of grains in the nebula, and critical velocity for sticking, indicates that, in contrast to the hibonite-bearing aggregates of corundum grains, the hibonite-free corundum aggregates could not have formed in the slowly cooling nebular region with solar composition. We suggest instead that such aggregates formed near the protosun, either in a region that stayed above the condensation temperature of hibonite for a long time or in a chemically fractionated, Ca-depleted region, and were subsequently physically removed from this hot region, e.g., by disk wind.

Original languageEnglish
Pages (from-to)1249-1265
Number of pages17
JournalMeteoritics and Planetary Science
Issue number7-8
Publication statusPublished - 2007


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