igneous
Weathered basalt or andesite
Fine-grained volcanic rock, likely basaltic-andesite; chiefly plagioclase feldspar, pyroxene, and possibly olivine or volcanic glass
AI-generated identification · may be incorrectDark brown-gray, porous and strongly weathered, with dull to slightly earthy luster and no obvious large crystals; hardness about 5–6 Mohs, massive texture, negligible cleavage, and specific gravity roughly 2.7–3.1 when unweathered
Identified More igneous →
Explore Weathered basalt or andesite in the encyclopedia →Identify your own rocks.
Get a report just like this from any photo, free.
Physical properties
Dark brown-gray, porous and strongly weathered, with dull to slightly earthy luster and no obvious large crystals; hardness about 5–6 Mohs, massive texture, negligible cleavage, and specific gravity roughly 2.7–3.1 when unweathered
Formation & geological history
Formed when lava cooled rapidly at or near Earth’s surface, probably during the Cenozoic or older volcanic activity; the rusty-brown color and cavities reflect oxidation and weathering
Uses & applications
Used as aggregate, road stone, riprap, and occasionally landscaping material; generally not suitable for jewelry except as a lapidary or display specimen
Geological facts
Basalt is the most abundant volcanic rock on Earth and commonly contains vesicles—gas-bubble cavities—that may later be filled by zeolites, calcite, or quartz
Field identification & locations
Identify by its dense volcanic texture, dark mafic color, fine grains, and vesicles; common in volcanic regions, including oceanic crust, Hawaii, Iceland, Mexico, and the western United States. A definitive identification requires a fresh surface or thin-section/petrographic testing
