phe·no·cryst (f  n -kr st )n. A conspicuous, usually large, crystal embedded in porphyritic igneous rock. phe no·crystic adj. |
phenocryst [ˈfiːnəˌkrɪst ˈfɛn-]
n
(Earth Sciences / Geological Science) any of several large crystals that are embedded in a mass of smaller crystals in igneous rocks such as porphyry
[from pheno- (shining) + crystal]
| phenocryst (fn-krst) 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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