ES2 Metamorphic Rocks - Metamorphic Microstructures #22
Rotational porphyroblast (syn-kinematic).
This garnet shows a double spiral pattern of graphite and quartz inclusions which indicate that it rotated clockwise relative to the external foliation during growth, through a total angle of about 225°. Note that the internal and external fabrics are continuous across the ends of the spiral arms, and that pressure-shadow material is caught up in the garnet spiral in the form of larger quartz grains in embayments and inclusions.
Plane-polarised light. Field of view is 2.5 mm across.
Garnet-mica schist, Hunza Karakoram.
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DJW - August 1997