igneous
Porphyritic Basalt or Porphyry
Porphyritic Igneous Rock
Hardness of 6-7 on the Mohs scale, dark grey to black groundmass with distinct pink or reddish phenocrysts (typically feldspar), dull to sub-vitreous luster, fine-grained aphanitic matrix with larger crystal inclusions, specific gravity around 2.7-3.0.
Identified More igneous →
Explore Porphyritic Basalt or Porphyry in the encyclopedia →Identify your own rocks.
Get a report just like this from any photo, free.
Physical properties
Hardness of 6-7 on the Mohs scale, dark grey to black groundmass with distinct pink or reddish phenocrysts (typically feldspar), dull to sub-vitreous luster, fine-grained aphanitic matrix with larger crystal inclusions, specific gravity around 2.7-3.0.
Formation & geological history
Formed through a two-stage cooling process in volcanic or shallow intrusive environments. Magma first cools slowly deep underground, forming larger crystals (phenocrysts), then erupts or moves closer to the surface, cooling rapidly to form the fine-grained matrix.
Uses & applications
Used primarily as decorative aggregate, dimension stone, or as a specimen for educational and rock-collecting purposes.
Geological facts
Porphyry was extensively quarried in ancient Rome, particularly the 'Imperial Porphyry' from Egypt, which was prized for its royal purple-red color and reserved exclusively for monuments and royalty.
Field identification & locations
Easily identified by its contrasting texture of large, distinct crystals embedded in a much finer-grained dark background. Commonly found in glacial drift, riverbeds, and volcanic regions worldwide.
