A metallographic study of the angra dos Reis (iron) meteorite

Abstract

SummaryThe Angra dos Reis (iron) has been studied metallographically and an attempt has been made to discuss the circumstances under which the following elements of structure formed: clear etching and frosty etching kamacite, decorated Neumann lines, giant rhabdites, plate rbabdites, rhabdite clusters, microrhabdites, cohenite, and remelted troilite. The remelted troilite is taken to indicate a shock event. However, since there are no metallographically visible indications of shock in the kamacite and since the back reflection X-ray diffraction pattern shows only very faint Debye-Scherrer arcs superimposed on a pattern of sharp spots, it is concluded that the shock event took place at a temperature that allowed shock effects to anneal out of the kamacite almost completely. A submicroscopic precipitate in the metallic matrix is observable with the electron microscope and may represent the final precipitation of phosphide from shocked kamacite.