Nuclear Abundance Rules and the Composition of Meteorites

Abstract

Many years ago the author was able to show that the abundances of nuclear species, as estimated from the chemical composition of meteorites, followed certain regularities which indicated that chemical fractionation processes have not completely obscured the primeval abundance ratios of the elements. The regularities can be expressed as rules. They are manifested to a different degree in the different types of meteorites and they give some indication as to which type of meteoritic material can be considered the most primeval.

On the basis of these rules the composition of Type I carbonaceous chondrites shows less fractionation than that of any other type of meteorites. As was discussed by many workers, differences in volatility were probably the main cause of fractionation. Should further astronomical observations continue to indicate an iron enrichment in all types of stony meteorites, then differences in volatility could also be considered the main type of cause of this fractionation. The enrichment of Fe, however, would have to have occurred at a much earlier stage than the fractionation indicated by the composition of ordinary chondrites as compared to Type I carbonaceous chondrites.