The mode of formation of Neumann bands. Part I.–The mechanism of twinning in the body-centred cubic lattice

Abstract

1. The existence of Neumann lamellæ as a characteristic feature of hexahedral meteoric iron and of the kamacite of octahedral meteorites has been known for many years. The traces of these lamellæ upon polished and etched surfaces were at first regarded as Widmanstätten figures; but it was shown by Neumann that they were distinct from such figures, that they were character­ istic of single cubic crystals, and that their outcrops upon a cube face, which he determined, were inconsistent with the assumption that they were octahedral lamellæ. Neumann, Tschermak and other mineralogists inferred from the geometrical relations between the outcrops of the bands that they were a consequence of an interpenetrating-cube twin structure within the meteorite, of a type known to occur in various minerals, e. g ., in fluor spar.