igneous
Porphyritic volcanic rock, possibly porphyritic andesite
Likely andesite porphyry; exact identification requires close examination
AI-generated identification · may be incorrectRounded, weathered specimen with a reddish-brown fine-grained matrix and dark elongated mineral patches that may be phenocrysts or inclusions. Andesite typically has Mohs hardness around 6, a dull to slightly lustrous surface, and a fine-grained groundmass; crystal structure is not visible overall.
Identified More igneous →
Explore Porphyritic volcanic rock, possibly porphyritic andesite in the encyclopedia →Identify your own rocks.
Get a report just like this from any photo, free.
Physical properties
Rounded, weathered specimen with a reddish-brown fine-grained matrix and dark elongated mineral patches that may be phenocrysts or inclusions. Andesite typically has Mohs hardness around 6, a dull to slightly lustrous surface, and a fine-grained groundmass; crystal structure is not visible overall.
Formation & geological history
Likely formed when magma cooled in two stages: larger crystals formed first, then the remaining melt cooled rapidly. Andesitic rocks are commonly associated with volcanic arcs, generally ranging from recent to ancient geological ages.
Uses & applications
Primarily a geological or collecting specimen; andesite is also used locally as aggregate, paving stone, and building stone.
Geological facts
Porphyritic texture records contrasting cooling rates and is common in volcanic rocks.
Field identification & locations
Look for distinct crystals set in a much finer matrix; the dark patches in this image are not clear enough to identify confidently. Andesite is common in volcanic regions, including the Andes and island arcs.
