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Related to Porphyroblasts: Porphyroblastic Texture


A large crystal that is surrounded by a fine-grained matrix in a metamorphic rock and forms from the recrystallization of existing mineral crystals during metamorphism.

[porphyr(y) + —blast.]
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Large metamorphic minerals (e.g., porphyroblasts such as biotite, garnet, andalusite and staurolite) that contain passive inclusions are extraordinarily important because they are utilized in assessing the tectonic, metamorphic, and structural history of the mid- to deep-crustal levels of orogenic belts.
They show jointing and intense fracturing, deformation and deflection of the main foliation of the rock around most garnet porphyroblasts. In some cases, a strong mylonitic deformation evidenced by lengthening and stretching of quartz, among others, is observed.
The late schistosity in the sedimentary rocks, defined by muscovite and biotite, wraps around cordierite porphyroblasts, which contain relicts of the earlier phyllitic cleavage (Thorne and Lentz 2001; Park et al.
Staurolite forms honey-brown large prismatic porphyroblasts which quite frequently reach up to 1.2 cm across and 12 cm in length, elongated along the schistosity and usually displaying reaction rims.
The amphibolite is porphyroblastic and contains porphyroblasts of hornblende.
Albite (Ab) and Grt2 (mineral abbreviations from Whitney and Evans, 2010) are porphyroblasts mainly syn-kinematic with the S2 and frequently helicitic, including a previous foliation (S1) (Figs.
The graphite occurs within "fairly homogeneous, quartz-graphite schist, incorporating minor "porphyroblasts" of muscovlte crystals and small lenses of extremely fine sillimanite".
and Speck, P.J.H.R.: 1994, The kinematic interpretation of obliquely-transected porphyroblasts: an example from the Trois Seigneurs Massif, France, J.
Migmatization is widespread, resulting in the formation of plagioclase and potassium-feldspar porphyroblasts and occasionally charnockitic leucosomes, also of small granitoid veins and bodies.