The mode of formation of Neumann bands. Part II.–The evidence that the bands are twins

Abstract

1. Any discussion of the significance of Neumann bands must involve the geometrical relationships between them and the matrix. The orientation of the cube lattice of a meteorite having been determined by X-ray or other methods, a section parallel to a cube face can be cut, polished and etched, and the angles which the traces of the Neumann bands make with the sides or the diagonals of the cube face can be measured. If the bands are parallel to the twelve planes of the icositetrahedron {112}, their traces will lie in the directions shown in fig. 5, PVUT representing the orientation of the cube face. The spatial relationships of the planes producing such {112} traces can be visualised by means of fig. 6, an isometric projection of a cube, in which the planes producing the traces shown in fig. 5 are indicated by their traces on three mutually perpendicular planes, e. g ., PVUT (010), PTQX (001) and PXWV (100).