Kamacite–Taenite Relationships in Iron Meteorites

Abstract

A NUMBER of investigators^1–3 have used the method of electron probe X-ray microanalysis in the examination of metallic meteorites. For those simple octahedrites which are free of visible thermal metamorphism there is general agreement that the various morphological forms of taenite are distinctly non-homogeneous with respect to nickel, whereas the bulk of the kamacite is of more uniform nickel content, although there is a decrease of nickel within the kamacite where it comes into contact with taenite^1,3. Extensive measurements of this effect have been made by Agrell, Long and Ogilvie³ on a sample of the Canyon Diablo meteorite, for which they found a nickel content of 6.8 ± 0.2 per cent for the bulk kamacite as compared with about 5.7 at the interface. In the machine used by Agrell, Long and Ogilvie the X-rays could be collected in a direction lying in the plane which contained the normal to the specimen surface and the intersection of the kamacite–taenite boundary with the surface. This simple geometry minimizes the anomalous effects which can arise if X-rays generated in one phase are absorbed by passage through another phase.