18 December 1987
Vol 238, Issue 4834

About The Cover

Image of the core of a crystallographic dislocation in grossular garnet (approximate composition Ca3Al2Si3O12) obtained by high-resolution transmission electron microscopy. The two parallel yellow lines are partial dislocations, separated by a core region of stacking fault. Perfect, unfaulted crystal structure surrounds the defect on the outside of the partial dislocations. The width of the fault corresponds to about 6 nanometers, or approximately 5 unit cells of garnet structure. See page 1695. [Computer processing of the image is by P. R. Buseck and A. Rimsky, Laboratoire de Mineralogie-Cristallographie, U.A. 09, Centre National de la Recherche Scientifique, Universités P. M. Curie and Paris, 7 Paris, France]