Hydrolytic weakening in quartz has been extensively demonstrated by experimental deformation of single crystals and aggregates. This paper describes the deformation and recrystallization microstructures and preferred orientations of quartz in a mylonite zone separating granulite facies (0.2% H2O) from amphibolite facies (1.0% H2O) acid gneisses. The transition from slightly deformed country rock on both sides to the ultimate product of mylonitization (a phyllite) is described and the following major differences are noted: 1. (1) The strain prior to recrystallization is higher on the granulite side. 2. (2) Misorientations across deformation-band boundaries are much higher on the granulite side. 3. (3) Subgrains and new grains are considerably smaller at the same stage of recrystallization on the granulite side. 4. (4) Preferred orientation of  developes more rapidly with respect to strain on the amphibolite side. 5. (5) There is a closer orientation relationship between host and recrystallized (new) grains on the granulite side. The microstructures and preferred-orientation development on both sides are related to concurrent ductile deformation, dynamic recovery and recrystallization processes. The differences between the two sides is attributed to the difference in bulk H2O content of the rocks and a resultant difference in strain rate. The suggested effect of water on recovery processes is favoured over its possible role in slip processes.