igneous
Weathered basaltic rock fragment
Basalt, likely vesicular or altered basalt; primarily plagioclase and pyroxene
AI-generated identification · may be incorrectDark brown-gray, fine-grained, dull to slightly earthy luster, with possible subtle vesicles and weathering rind; hardness about 5–6 Mohs, generally massive with no obvious cleavage, specific gravity about 2.8–3.0.
Identified More igneous →
Explore Weathered basaltic rock fragment in the encyclopedia →Identify your own rocks.
Get a report just like this from any photo, free.
Physical properties
Dark brown-gray, fine-grained, dull to slightly earthy luster, with possible subtle vesicles and weathering rind; hardness about 5–6 Mohs, generally massive with no obvious cleavage, specific gravity about 2.8–3.0.
Formation & geological history
An extrusive igneous rock formed when mafic lava cooled rapidly at or near Earth’s surface, commonly during volcanic eruptions. The brown surface reflects oxidation and chemical weathering; its exact age cannot be determined from the image.
Uses & applications
Basalt is widely used as crushed aggregate, road material, riprap, dimension stone, and occasionally in landscaping; ordinary fragments have negligible jewelry value.
Geological facts
Basalt is the most common volcanic rock and makes up much of oceanic crust. It commonly contains microscopic crystals that may be difficult to see without magnification.
Field identification & locations
Identify it by its dark color, fine texture, high density, and lack of visible quartz; a streak test is usually gray, and it should not fizz with dilute hydrochloric acid unless carbonate alteration is present. Common in volcanic regions and glacial or stream deposits worldwide.
