Porphyritic is an adjective used in
geology, specifically for
igneous rocks, for a rock that has a distinct difference in the size of the crystals, with at least one group of crystals obviously larger than another group. Porphyritic rocks may be
aphanites or
extrusive, with large crystals or
phenocrysts floating in a fine-grained
groundmass of non-visible crystals, as in a porphyritic
basalt, or
phanerites or
intrusive, with individual crystals of the groundmass easily distinguished with the eye, but one group of crystals clearly much bigger than the rest, as in a porphyritic
granite. Most types of igneous rocks may display some degree of porphyritic texture. One main type of rock that has a porphyritic texture are
porphyry, though not all porphyritic rocks are porphyries.