Abstract

Electron diffraction patterns of chrysotile asbestos fibrils should have the 2mm symmetry of a rotation photograph because the layers in the structure are curled as cylinders. The way in which the fibril orientation affects the diffraction patterns is considered theoretically. The departures from ideal symmetry attributable to specimen orientation are noted: they affect mainly the h00 reflections close to the fibre axis. Actual diffraction patterns show a consistent difference in the separation of the h0l-h0 pairs on the upper levels, and 0l-0 pairs on the lower. The experimental conclusion Yada (1979). Can. Mineral. 17, 679-691 that this difference is not an effect of specimen orientation is confirmed theoretically but its cause remains obscure.