igneous
Vesicular basalt (scoriaceous basalt)
Basalt, predominantly plagioclase feldspar, pyroxene, and olivine; iron-oxide-rich alteration may cause the reddish-brown color
AI-generated identification · may be incorrectDark reddish-brown, fine-grained, dull to slightly earthy luster, with irregular vesicles and rough fracture; hardness about 5–6 Mohs, no obvious cleavage, and typical specific gravity around 2.7–3.0.
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Physical properties
Dark reddish-brown, fine-grained, dull to slightly earthy luster, with irregular vesicles and rough fracture; hardness about 5–6 Mohs, no obvious cleavage, and typical specific gravity around 2.7–3.0.
Formation & geological history
An extrusive volcanic rock formed when fluid basaltic lava cooled rapidly at or near the surface, trapping gas bubbles; commonly Quaternary to Recent, though basalt occurs throughout geologic time.
Uses & applications
Used as crushed aggregate, road material, riprap, and occasionally landscaping stone; attractive pieces may be collected, but this specimen has little gem value.
Geological facts
The cavities indicate gas-rich lava, while the rusty color commonly reflects oxidation of iron-bearing minerals. It may be confused with reddish scoria or weathered iron-rich volcanic rock.
Field identification & locations
Identify it by its dark fine-grained matrix, vesicles, heavy weight, and lack of glassy conchoidal fracture; common in volcanic regions such as Hawaii, Iceland, the western United States, and oceanic islands.
