- any of the conspicuous crystals in a porphyritic rock.
Origin of phenocryst
Dictionary.com Unabridged Based on the Random House Unabridged Dictionary, © Random House, Inc. 2018
- any of several large crystals that are embedded in a mass of smaller crystals in igneous rocks such as porphyry
C19: from pheno- (shining) + crystal
- A large crystal that is surrounded by a finer-grained matrix in an igneous rock. Phenocrysts are usually the first crystals to form from a cooling magma, and therefore have sufficient room to grow to a large size. They are analogous to porphyroblasts in metamorphic rock.
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