Chemical classification of iron meteorites—VIII. Groups IC. IIE, IIIF and 97 other irons

Abstract

Concentrations of Ni, Ga, Ge and Ir in 106 iron meteorites are reported. Three new groups are defined: IC, IIE and IIIF containing 10, 12 and 5 members, respectively, raising the number of independent groups to 12. Group IC is a cohenite-rich group distantly related to IA. Group IIE consists of those irons previously designated Weekeroo Station type and five others having similar compositions though diverse structures. The IIE irons are compositionally similar to the mesosiderites and pallasites, and the three groups probably formed at similar heliocentric distances. The mixing of the globular IIE silicates with the metal probably occurred during shock events. Group IIIF is a well-defined group of low-Ni and low-Ge irons. The compositions of these groups are summarized as follows: Group Ni (%) Ga (ppm) Ge (ppm) Ir (ppm) IC 6.1–6.8 42–54 85–250 0.07–10 IIE 7.5–9.7 21–28 62–75 0.5–8 IIIF 6.8–7.8 6.3–7.2 0.7–1.1 1.3–7.9 Data are reported on a number of anomalous irons including an interesting cluster of 5 plessitic octahedrites and ataxites with Ge/Ga atomic ratios between 10 and 16, among the highest values known in iron meteorites. Dermbach, at 42%, has the second highest Ni concentration known in an iron meteorite. The composition of metal and slicates in Mundrabilla indicate that it and its close relative. Waterville, are anomalous members of group IA. Several additional irons which appear to be mislabelled fragments of Canyon Diablo and Toluca are discussed.