Magnetite in CI chondrites

On the basis of 939 measurements of the CI chondrites, their magnetite contents have been determined to be: Alais, 8.9±0.9%, Ivuna, 11.1±0.3%, Orgueil, 11.0±0.4%, Revelstoke, 9.4% and Tonk, 8.5%. Standard statistical analysis of the data indicates the existence of two subgroups, one comprised of Ivuna and Orgueil, the other of Alais, Revelstoke, and Tonk. While we are not proposing a change in classification, it is clear that distinctive differences exist between the two subgroups. The precision of the method is ≈±3% so that the standard deviations listed reflect the extent of actual variation in magnetite distribution. The wide range, from 6 to nearly 50% Fe3O4, in previous estimates of the magnetite content of Orgueil is due to experimental error, not to a real heterogeneity.

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