Concentrations of 26 elements were determined by replicate neutron-activation analysis in 66 ordinary chondrites (22 H, 20 L, 17 LL, 2 intermediate between H and L and 5 intermediate between L and LL). Olivine and kamacite compositions were determined in adjacent samples; about 20% of the chondrites contain kamacite or olivine grains with aberrant compositions > 3s from the mean. The sample set was biased in favor of the reduced, siderophile-rich and oxidized, siderophile-poor members of the groups and in favor of chondrites reported to have unusual compositional features. Several chondrites were reclassified: e.g., the photographed fall, Innisfree, is L, not LL; Albareto is LL, not L; and Xingyang and Zhovtnevyi are H6, not H5.

On a plot of kamacite Co concentration versus Fa content of olivine, there is a hiatus between H and L, but no hiatus between L and LL. Five chondrites (Bjurböle, Cynthiana, Knyahinya, Qidong, Xi Ujimgin) fall between the main L and LL clusters. Cosmic-ray and U, Th-He outgassing age data do not demonstrate relationships to either group. Our siderophile data support the previous group assignments of unequilibrated chondrites in all cases but two: Bremervörde and Tieschitz have siderophile levels intermediate between H and L.

Our mean group compositions are in good agreement with those previously reported. We confirm that the Co/Ni ratio decreases about 5% through the H-L-LL sequence and that Na and Mn abundances are about 7% lower in H than in L and LL. Selenium and Zn show similar abundances in the three groups; the very low (~0.1 × CI) Zn abundance is attributed to condensation as fine, ZnS aerosols that inefficiently settled to the midplane. Abundances of V and Cr decrease by only ~2% between H and LL; thus, only a small fraction was in nebular siderophile components.

With the exception of highly volatile Br, no significant differences in abundance are observed among the petrographic types of each group. This conflicts with earlier conclusions that intertype differences (including a systematic increase in siderophile abundance with increasing type) are present. The small differences we observed are attributable to anomalously low or high contents of one or two phases (generally metal and/or troilite) in a few replicates. The absence of a relationship between composition and petrographic type is consistent with models calling for the progressive thermal metamorphism of primitive unequilibrated materials to produce the observed spectrum of petrographic grades, and places narrow limits on the relative accretion efficiencies of nebular components in those models calling for the sequential accretion of nebular materials.