The stress-sensitivity of quartz in tectonites

Petrofabric investigation of five crossbedded quartzites shows an essentially isotropic fabric in three cases, and preferred orientation together with parallel texture in the remaining two. Crossbedding is undistorted in all five. Recrystallization by solution and re-deposition could satisfactorily explain the three isotropic fabrics. Low-magnitude shear of short duration, coupled with extremely sensitive response of quartz to deformation, is the preferred explanation for the quartzites showing preferred orientation.At a higher metamorphic level in a sheared granite, stress-sensitive quartz and stress-insensitive feldspar are contrasted and, in view of their analogous crystal structures, the apparent anomaly in deformation behavior is noted.With 2 figures.