Pseudotachylite, a very fine grained glasslike rock, forms veins and the matrix of breccias in the core and overturned collar rocks of the Vredefort ring. The cataclastic character of coarse breccias, of which pseudotachylite forms the matrix, persists to microscopic sizes where individual mineral grains are seen to be laced by thin veins composed of crushed mineral debris. Only locally, and only in granitic rocks, is there evidence suggestive of fusion. Mixing of crushed mineral debris during injection or spallation into fractures formed the common type of pseudotachylite. Well-developed basal deformation lamellae in quartz of rock fragments in pseudotachylite and in the wall rock indicate high strain rates and transient pressures above 35 kb, and possibly above 100 kb, before or during pseudotachylite formation. Deformation of other minerals includes formation of multiple sets of planar structures in feldspars and mica, and a single set of planar structures parallel to {101 }? in amphibole. Micas and amphiboles underwent further breakdown to mattes of unoriented minute grains before incorporation in pseudotachylite. The mode of occurrence of pseudotachylite and association with shock deformation features are shared by microbreccias in carbonate rocks of cryptoexplosion structures elsewhere that are not related to magmatic activity. This supports the belief that such breccias, including Vredefort pseudotachylite, are the products of shock deformation, probably related to impact events.