The Collaborative International Dictionary
Porphyritic \Por`phy*rit"ic\, a. [Cf. F. porphyritique.] (Min.) Relating to, or resembling, porphyry, that is, characterized by the presence of distinct crystals, as of feldspar, quartz, or augite, in a relatively fine-grained base, often aphanitic or cryptocrystalline.
a. 1 of or pertaining to porphyry 2 (context geology English) containing large crystals in a fine mass of material
adj. (of rocks) consisting of porphyry or containing large crystals in a fine groundmass of minerals
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.
Usage examples of "porphyritic".
There are the pink and red Syenites, porphyritic granite, yellow granite, grey granite, both black granite and white, and granites veined with black and veined with white.
It showed at once a complete change of formation: the sides were painted with clays of variegated colours, crystallized lime and porphyritic conglomerates, tinted mauve-purple as if by manganese.
On the left bank a porphyritic block, up whose side a mule can be ridden, is disposed in a slope of the palest and most languid of greens, broken by piles of black rock so regular as to appear artificial.
From the raised and metalled bank, upon which the Burj stands, we descended to the broad mouth of the Wijh valley, draining the low rolling blue-brown line of porphyritic hillocks on the east.
The staple material, porphyritic trap, shows scatters of quartz and huge veins, mostly trending north-south: large trenches made, according to the guides, by the ancients, and small cairns or stone piles, modern work, were also pointed out to us.
Skirting the bleak shores of Patagonia in a single narrow sierra, the Andes enter Chile, rising higher and higher till they culminate in the gigantic porphyritic peak of Aconcagua.
Patagonia in a single narrow sierra, the Andes enter Chile, rising higher and higher till they culminate in the gigantic porphyritic peak of Aconcagua.
It is made of a remarkable variety of porphyritic diorite that resembles breccia.
The bedded volcanic rocks which form a series of ridges trending north-west comprise porphyritic basalts, andesite, and, near Port Luchdach, brownish trachyte.
Porphyritic tuffs and massive limestone compose the western chain of the Andes above Lima, while in the Oroya Valley we find carbonaceous sandstones.