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porphyry




porphyritic granite
Porphyritic granite
A hard igneous rock having many large crystals (phenocrysts) set in a very fine-grained matrix, occurring in dikes and sills. More generally, rocks are said to have a porphyritic texture if they contain some phenocrysts in a finer-grained matrix (e.g., porphyritic granite, as shown here).


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   • GEOLOGY AND PLANETARY SCIENCE