igneous
Porphyry (Polished Pebble)
Porphyritic Rhyolite / Andesite
Hardness 6-7 on Mohs scale. Features distinct pink/reddish feldspar phenocrysts (crystals) embedded in a fine-grained dark reddish-brown to grayish groundmass. Vitreous to dull luster, highly smooth polished surface.
Identified More igneous →
Explore Porphyry (Polished Pebble) in the encyclopedia →Identify your own rocks.
Get a report just like this from any photo, free.
Physical properties
Hardness 6-7 on Mohs scale. Features distinct pink/reddish feldspar phenocrysts (crystals) embedded in a fine-grained dark reddish-brown to grayish groundmass. Vitreous to dull luster, highly smooth polished surface.
Formation & geological history
Formed in a two-stage cooling process of magma: large phenocryst crystals form slowly at depth, followed by rapid cooling near or at the surface forming the fine-grained matrix. Often Precambrian or Paleozoic in age.
Uses & applications
Used for decorative stone, tumbled gemstone art, lapidary projects, and ornamental gravel or polished display specimens.
Geological facts
Porphyry rocks were historically prized by ancient civilizations; Red Imperial Porphyry from Egypt was exclusively reserved for Roman emperors for sarcophagi and monuments.
Field identification & locations
Identified in the field by its classic 'pinstripe' or 'starry night' porphyritic texture—distinct rectangular, lighter-colored feldspar crystals floating within a fine-grained, darker igneous matrix. Frequently found around Lake Superior, Canada, and ancient volcanic terranes.
