Porphyroblasts and Rotated Porphyroblasts - These occur when a large mineral crystal in a metamorphic rock grows within the finer grained groundmass. These are commonly garnet as seen above, but other minerals can also grow as porphyroblasts. Rotated porphyroblasts are often important in analyzing strain and deformation planes that the mineral and outcrop were subjected to as they grew, leaving a rotated appearance.
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