High voltage electron petrography of olivine crystals from a peridotite deformed experimentally at high temperature and confining pressure shows that the deformation lamellae visible optically in petrographic thin sections consist of narrow zones of closely spaced edge dislocations. The peridotite specimen was deformed in the regime where pencil glide parallel to [100] dominates flow in olivine, and areas selected from the petrographic section were thinned to electron transparency by low-angle ion bombardment. Planar arrays of parallel edge dislocations with Burgers' vector [100] on the planes normal to [010] and [011] were found. These arrays appear identical in all important respects to slip bands in metals and to the dislocation model for photoelastic deformation lamellae proposed originally to explain such features in quartz.

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