Definition of porphyroclast in English:

porphyroclast

Pronunciation /ˈpɔːfɪrəklɑːst/ /ˈpɔːfɪrəklast/

noun

Geology
  • A relatively large grain remaining in a finer groundmass in a rock which has undergone dynamic metamorphism.

Origin

1930s. From porphyro- + -clast, after porphyroclastic.