porphyroclastn.
/ˈpɔːfᵻrəklɑːst/, /ˈpɔːfᵻrəklast/, U.S. /ˈpɔrfəroʊˌklæst/ Geology.
A relatively large grain remaining in a finer groundmass in a rock which has undergone dynamic metamorphism.
ΘΚΠ
the world > the earth > structure of the earth > constituent materials > rock > texture or colour > [noun] > texture > having embedded crystals > crystalline substance in
mica1681
kernel1839
phenocryst1889
idioblast1920
porphyroblast1920
porphyroclast1932
poikiloblast1944
1932 Jrnl. Geol. (Chicago) 40 629 The rocks containing occasional porphyroclasts are the most common varieties in the mylonite zone.
1975 Nature 10 Apr. 489/2 Xenoliths with variable microscopic fabric patterns containing porphyroclasts seem to have suffered increasingly intense shearing stresses through progressive deformation.
1993 Jrnl. Petrol. 34 431 The early high P-T granulite facies minerals in most of these rocks are preserved only as relict porphyroclasts set in a recrystallized matrix of lower-grade, amphibolite/granulite facies minerals.
This entry has been updated (OED Third Edition, December 2006; most recently modified version published online March 2022).
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n.1932