porphyroblast

(redirected from Porphyroblasts)
Also found in: Encyclopedia.
Related to Porphyroblasts: Porphyroblastic Texture

por·phyr·o·blast

 (pôr-fîr′ə-blăst′)
n.
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.]
Mentioned in ?
References in periodicals archive ?
The member here consists of massive hornfels, in which the cleavage has been largely annealed, and originally finer-grained pelitic units display strongly pitted surfaces due to weathering of coarse retrogressed cordierite porphyroblasts.
Also displayed are whitish or greyish colour, polymodal grainsized distribution pattern of mostly fine to medium grains with occasional porphyroblasts and distinct linear and planar fabric, highlighted by the laminar structures.
GROWTH OF CENTIMETER-SCALE GARNET PORPHYROBLASTS AT THE
These are greenish-grey (5G 4/1-5G 6/1), fine-grained, metavolcaniclastics characterised by a sub-conchoidal to sub-hackly fracture, laminae, small rock clasts and oxidised pyrite porphyroblasts.
Migmatization is widespread, resulting in the formation of plagioclase and potassium-feldspar porphyroblasts and occasionally charnockitic leucosomes, also of small granitoid veins and bodies.
Extremely large cordierite porphyroblasts up to 10 cm in length now pseudomorphed by pinite/sericite are present in muscovite-rich rocks from the extreme southwestern part end of the study area.
Mica schist have a paragenesis of quartz + muscovite + biotite with minor garnet, chloritoid and plagioclase, and locally andalusite porphyroblasts cutting the [S.
8:45 INVESTIGATION OF METAMORPHIC CONDITIONS ASSOCIATED WITH THE GROWTH OF CENTIMETER-SCALE GARNET PORPHYROBLASTS AT THE GARNET HILL LOCALITY, WEST-CENTRAL GEORGIA**, Nelson Spratt IV* and C.
The coarse-grained peak assemblage with equidimensional porphyroblasts has probably formed under isotropic or weak unisotropic stress conditions.
A contact aureole surrounding the intrusion is indicated by the presence of biotite and cordierite porphyroblasts in the pelitic rocks (Seal et al.