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A large crystal that is surrounded by a fine-grained matrix in a metamorphic rock and forms from the recrystallization of existing mineral crystals during metamorphism.
[porphyr(y) + —blast.]
American Heritage® Dictionary of the English Language, Fifth Edition. Copyright © 2016 by Houghton Mifflin Harcourt Publishing Company. Published by Houghton Mifflin Harcourt Publishing Company. All rights reserved.