ES2 Metamorphic Rocks - Metamorphic Microstructures #6
Recovery and recrystallisation in quartz
The large, strongly-strained quartz grain in the centre shows undulose extinction. Rather than varying smoothly across the grain, however, the extinction reveals a patchwork of subgrains. These result from the process of recovery, in which dislocations migrate to form planar arrays separating relatively strain-free domains with a small angular mismatch. Above and below, quartz has recrystallised into new, smaller grains. These in turn have begun a second cycle of deformation - their boundaries are no longer polygonal but interlobate.
Crossed polars. Field of view 1.75 mm.
Moine meta-sandstone Ø500, Scotland
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DJW - August 1997