igneous
Weathered volcanic rock, likely basalt
Basalt; chiefly plagioclase feldspar, pyroxene, and commonly olivine or alteration minerals
AI-generated identification · may be incorrectFine-grained, dark gray to greenish-brown exterior with rusty weathering and faint vesicular or mottled texture; hardness about 6–7 Mohs, dull to slightly vitreous luster, no obvious cleavage, and typical specific gravity around 2.8–3.0.
Identified More igneous →
Explore Weathered volcanic rock, likely basalt in the encyclopedia →Identify your own rocks.
Get a report just like this from any photo, free.
Physical properties
Fine-grained, dark gray to greenish-brown exterior with rusty weathering and faint vesicular or mottled texture; hardness about 6–7 Mohs, dull to slightly vitreous luster, no obvious cleavage, and typical specific gravity around 2.8–3.0.
Formation & geological history
Basalt forms when low-silica mafic lava cools rapidly at or near Earth’s surface, commonly in volcanic fields, oceanic crust, and flood-basalt provinces. Its exact age cannot be determined from the photograph.
Uses & applications
Used widely as crushed aggregate, road base, railroad ballast, riprap, and building stone; attractive polished pieces are sometimes collected, though this specimen appears primarily of field-collecting interest.
Geological facts
The green and brown colors may reflect chlorite, epidote, iron oxides, or other alteration products. A fresh broken surface should be darker and finer-grained than the weathered rind.
Field identification & locations
Common in volcanic terrains worldwide, including Hawaii, Iceland, the Columbia River region, and oceanic islands. Confirm with a fresh fracture, lack of fizz in dilute acid, and possible weak attraction to a magnet if magnetite is present; exact identification from the image is provisional.
