porphyroblast
Sign in to savethumb|300px|Thin section of a garnet porphyroblast (black) in a mica schist that contains foliated trails of small inclusions (white and grey)
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thumb|300px|Thin section of a garnet porphyroblast (black) in a mica schist that contains foliated trails of small inclusions (white and grey)
A porphyroblast is a large mineral crystal in a metamorphic rock which has grown within the finer grained matrix. Porphyroblasts are commonly euhedral crystals, but can also be partly to completely irregular in shape.
Excerpted from Wikipedia’s “porphyroblast” article, available under the CC BY-SA 4.0 licence.
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