Porphyroid - definition of porphyroid by The Free Dictionary
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Metamorphic rock having porphyritic texture.
(Geological Science) (of metamorphic rocks) having a texture characterized by large crystals set in a finer groundmass
(Geological Science) a metamorphic rock having this texture
References in periodicals archive
Accordingly, the highest silver-copper-antimony grades are in those parts of the vein which are hosted by relatively ductile quartz-sericite phyllites on Levels 8 and 9 whilst lower grade mineralisation developed in parts of the vein hosted by competent porphyroids
(mostly on Level 13).