igneous
Weathered volcanic rock fragment
Likely andesite or basaltic-andesite; exact identification requires fresh surface and testing
AI-generated identification · may be incorrectFine- to medium-grained, gray-tan, dull to weakly earthy luster, with scattered dark and pale mineral grains; likely hardness about 5–6, nonfoliated, and lacking obvious cleavage. The rounded, abraded shape indicates transport or weathering.
Identified More igneous →
Explore Weathered volcanic rock fragment in the encyclopedia →Identify your own rocks.
Get a report just like this from any photo, free.
Physical properties
Fine- to medium-grained, gray-tan, dull to weakly earthy luster, with scattered dark and pale mineral grains; likely hardness about 5–6, nonfoliated, and lacking obvious cleavage. The rounded, abraded shape indicates transport or weathering.
Formation & geological history
An extrusive volcanic rock formed when lava cooled at or near Earth’s surface, probably during a Cenozoic volcanic episode; its precise age and source cannot be determined visually. It may have been deposited as alluvium or beach/stream gravel.
Uses & applications
Common volcanic aggregate is used in road base, concrete, riprap, and landscaping, but this weathered piece has little commercial or jewelry value.
Geological facts
Andesite commonly contains plagioclase with pyroxene and/or amphibole; basaltic-andesite is darker and more mafic. The surrounding material appears to be mixed volcanic sediment or coarse gravel.
Field identification & locations
Look for a dense, fine-grained texture, gray-to-dark color, and small white plagioclase crystals; a streak, magnetism, acid reaction, and fresh fracture help distinguish it from concrete or sedimentary rock. Common in volcanic regions and river or coastal deposits.
