Definition of porphyroblast in English:
porphyroblast
noun ˈpɔːfɪrə(ʊ)blastpôrˈfirəˌblast
Geology A larger recrystallized grain occurring in a finer groundmass in a metamorphic rock.
Example sentencesExamples
- Evidence of contact metamorphism of the wall-rock includes andalusite porphyroblasts enclosed in a fabric related to Caledonian nappe emplacement.
- The foliation in the lowest unit is locally overgrown by porphyroblasts of andalusite (now commonly altered to finegrained phyllosilicates) and by biotite.
- Such inclusions may be aligned, preserving evidence of the fabric in the rock when the porphyroblast grew.
- Cordierite in these two metamorphic belts forms rounded, opaque black to brown porphyroblasts typically less than 0.5 inch across.
- In contrast, 2 km to the NE on the southern side of the Dharlang Nala, there are kyanite grade assemblages with a weaker foliation, flattened symmetrically around garnet porphyroblasts.