Rhodium and osmium in iron meteorites

Abstract Rh and Os were quantified by instrumental neutron activation analysis in 106 iron meteorites. The data for Rh are the first extensive values to be reported for this element in iron meteorites. The Rh vs. Ni concentration plot allows for good spatial separation of groups IB, IC, IIA, IIB, IIC, IID, high-Ni IIICD, IVA and IVB. Low-Ni IIICD meteorites (Nandan and Cranbourne) seem to belong spatially to Group IA to which they were originally assigned. Os concentrations are strongly correlated with those of Ir. A plot of Os vs. Ni gives poorer group separations than that of Rh vs. Ni. Only in the cases of groups IB, IID, high-Ni IIICD and IVB are there convincing spatial separations. Once again, the low-Ni Nandan and Cranbourne fall within the IA field. Other data lend additional support to a previous proposal that Lamesa and Dayton be paired because of their similar chemical composition.