Definition of porphyroblast in English:
A larger recrystallized grain occurring in a finer groundmass in a metamorphic rock.
- Evidence of contact metamorphism of the wall-rock includes andalusite porphyroblasts enclosed in a fabric related to Caledonian nappe emplacement.
- 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.
- Example sentences
- Strongly foliated porphyroblastic politic gneiss forms a selvedge up to 100 m thick in sharp (but in some cases ductile) contact with peridotite on the northern margin of the Carratraca massif.
- The earliest porphyroblastic fabric is not restricted to the immediate metapluton surroundings.
Definition of porphyroblast in:
- US English dictionary