igneous
Tumbled basalt with vesicles and weathering
Basalt, a mafic volcanic rock dominated by plagioclase and pyroxene, commonly with olivine and iron oxides
AI-generated identification · may be incorrectDark gray-black, fine-grained, glassy-to-dull luster; likely Mohs 5–6, with irregular fracture and small vesicles. The orange-brown patches are probably weathered iron minerals or oxidized olivine; the specimen appears naturally rounded or tumbled.
Identified More igneous →
Explore Tumbled basalt with vesicles and weathering in the encyclopedia →Identify your own rocks.
Get a report just like this from any photo, free.
Physical properties
Dark gray-black, fine-grained, glassy-to-dull luster; likely Mohs 5–6, with irregular fracture and small vesicles. The orange-brown patches are probably weathered iron minerals or oxidized olivine; the specimen appears naturally rounded or tumbled.
Formation & geological history
Basalt forms when low-silica lava rapidly cools at or near Earth’s surface, commonly in oceanic crust, flood-basalt provinces, and volcanic islands. Its age cannot be determined from the photograph and may range from recent to billions of years.
Uses & applications
Used as aggregate, crushed stone, road base, riprap, building stone, and occasionally in landscaping or lapidary work. Common tumbled pieces have modest collector value.
Geological facts
Basalt is the most abundant volcanic rock and makes up much of the ocean floor. Vesicles record gas bubbles trapped during lava cooling, while rusty colors indicate oxidation.
Field identification & locations
Common worldwide, especially Hawaii, Iceland, the ocean floor, India’s Deccan Traps, and the Pacific Northwest. A streak, close inspection of grain size, and lack of metallic magnetism help distinguish it from slag or ironstone.
