phenocryst
/ˈfiːnoʊkrɪst/
noun
- A large, visible crystal in a volcanic rock that is surrounded by a finer-grained matrix.
- Phenocrysts form when magma cools slowly underground before a volcanic eruption.
- The rock's texture is porphyritic, with phenocrysts scattered throughout.
- The geologist identified a large phenocryst of feldspar in the lava sample.
Synonyms