igneous
Probable weathered basalt or andesite
Fine-grained mafic to intermediate volcanic rock; commonly plagioclase ± pyroxene, amphibole, and iron oxides
AI-generated identification · may be incorrectGray, dull to weakly earthy luster, apparently massive and fine-grained, with irregular weathered surfaces; estimated Mohs hardness 5–6 and specific gravity about 2.7–3.1. The image is insufficient to determine exact texture or mineralogy.
Identified More igneous →
Explore Probable weathered basalt or andesite in the encyclopedia →Identify your own rocks.
Get a report just like this from any photo, free.
Physical properties
Gray, dull to weakly earthy luster, apparently massive and fine-grained, with irregular weathered surfaces; estimated Mohs hardness 5–6 and specific gravity about 2.7–3.1. The image is insufficient to determine exact texture or mineralogy.
Formation & geological history
Formed when lava cooled at or near Earth’s surface, generally during the Cenozoic or older volcanic episodes; the specimen’s geological age and locality cannot be established visually.
Uses & applications
Common basalt and andesite are used as crushed aggregate, road stone, riprap, and dimension stone; ordinary hand specimens have little commercial value.
Geological facts
Basalt is the most abundant volcanic rock in Earth’s oceanic crust, whereas andesite is especially common in volcanic arcs above subduction zones.
Field identification & locations
Look for a hard, dense, fine-grained gray rock that may weakly attract a magnet if iron-rich; a streak, acid test, fresh broken surface, and hand lens would improve identification. Common worldwide in volcanic regions.
