porphyroblast


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Related to porphyroblast: Porphyroblastic Texture, Euhedral

porphyroblast

[pȯr′fir·ə‚blast]
(petrology)
A relatively large crystal formed in a metamorphic rock.
References in periodicals archive ?
The features of each type of garnet (FIGURE 5) are described in detail below, revealing not only the morphological type of garnet but also that the sections do not intersect porphyroblast centre.
Garnet porphyroblasts which contain inclusions of quartz and biotite are arranged parallel to dominant crenulation cleavage.
Two conflicting hypothesis have been postulated for the asymmetric inclusion trail geometries: porphyroblast rotation and non-rotation.
Well developed preferred vertical and horizontal orientations of both sigmoidal and millipede inclusion trails imply that their development involved limited or no relative rotations between porphyroblasts.
The earliest deformation event recognized in the Sutlej GHS at the level of the MCT is recorded by straight to sigmoidal (S1) inclusion trails of quartz + ilmenite in the cores of large garnet porphyroblasts.
Metabasites and associated rocks of the Arquia Complex in the study area are mainly represented by chlorite and actinolite to amphibole schists, the last of them with or without garnet porphyroblasts, with minor garnet-bearing or -absent amphibolites and subordinate amounts of serpentinized peridotites and metabasalts.
Like in the contact aureole of the mafic dykes in the Clarence Stream area, cordierite porphyroblasts in the host rocks of the Mohannes Granite show evidence of growth during deformation.
Internal foliation (S1) in Ab porphyroblasts is defined by graphitic inclusion trails and opaque minerals.
Migmatization is widespread, resulting in the formation of plagioclase and potassium-feldspar porphyroblasts and occasionally charnockitic leucosomes, also of small granitoid veins and bodies.
Optically continuous calcite layers are present between the garnet growth bands within some of the garnet porphyroblasts.