An investigation of some banded structures in metal crystals

Crystals of the native metals gold, silver and copper have been found which exhibit twinning on an octahedral plane of the spinel type. Metallurgists have described as twins the banded structures which are of very frequent occurrence in these metals when prepared commercially, as they resemble lamellar twinning in calcite and felspar very closely. A few quantitative measurements have been made to determine the relationship between such bands in a metallic crystal; but the value of the results depends on the correct determination of the orientation of the respective parts, and this can only be done by means of X-rays or by indirect methods such as the measurement of slip-bands, etching-pits, etc., which are not always trustworthy. McKeehan measured some structures resembling twins in nearly pure iron by obtaining reflections from the deeply etched surface of a wire mounted in a goniometer. He concluded that the crystals were twins in a crystallographic sense, the twin plane being of the form {211} and the twin axis of the form [111].