Structure and crystallographic texture of a metallic meteorite of octahedrite type (Gibeon)

A sample from the meteoritic iron Gibeon (fine octahedrite) has been studie d combining optical and scanning electron microscopy, crystallographic micr otexture by EBSP (Electron Back Scattered Patterns) and macrotexture by X-r ay diffraction. The sample (approx. 24x23x3 mm, 14.3 g) shows the classical Widmastatten structure of intersecting ferrite (kamacite) plates grown alo ng {111}(gamma) octahedric previous austenite (taenite) planes. Residual la yers of austenite are also seen between the ferrite plates as well as large r domains of more complex structures of bainitic type (plessite) produced b y the last fraction of austenite transformed during extra-terrestrial cooli ng. The sample structure shows few signs of impact modifications (Neumann b ands, etc.). Kamacite plates are divided in weakly misoriented (<2 degrees) subgranular domains. The measurement of individual orientations by EBSP or the macroscopic texture measurement show a single austenite orientation (a lthough with a nonnegligible dispersion around the average orientation) and a limited number of ferrite orientations compatible with the variants of t he Kurdjumov-Sachs orientation relationship.