igneous
Weathered gray rock, likely basalt or andesite
Fine-grained mafic to intermediate volcanic rock; likely basalt (plagioclase ± pyroxene, possibly altered)
AI-generated identification · may be incorrectDark gray, dull to weakly submetallic surface with pronounced weathering and cavities; likely hardness 5–6, massive fine-grained texture, and specific gravity about 2.7–3.0. The apparent layered lines may be surface fractures or adhered weathered material rather than true foliation.
Identified More igneous →
Explore Weathered gray rock, likely basalt or andesite in the encyclopedia →Identify your own rocks.
Get a report just like this from any photo, free.
Physical properties
Dark gray, dull to weakly submetallic surface with pronounced weathering and cavities; likely hardness 5–6, massive fine-grained texture, and specific gravity about 2.7–3.0. The apparent layered lines may be surface fractures or adhered weathered material rather than true foliation.
Formation & geological history
Formed when lava cooled at or near Earth’s surface, generally during the Cenozoic or older depending on locality; the specimen has subsequently undergone oxidation, abrasion, and chemical weathering.
Uses & applications
Common basalt and andesite are used as crushed aggregate, roadstone, riprap, and occasionally building stone; this heavily weathered piece has mainly educational or decorative value.
Geological facts
Volcanic rocks can develop vesicles that later fill with secondary minerals, producing pits and irregular textures like those visible here.
Field identification & locations
Identify basalt by its dark color, fine grain, lack of visible quartz, and high density; a hand lens and streak, hardness, and magnetism tests would help distinguish basalt from andesite or altered industrial slag. Common worldwide in volcanic regions.
