igneous
Weathered vesicular basalt (probable)
Basalt; primarily plagioclase, pyroxene, and often olivine
AI-generated identification · may be incorrectDark gray to rusty brown, fine-grained, rough, and locally vesicular with weathering cavities; typically dull to weakly lustered. Hardness about 5–6 Mohs, no obvious cleavage, and specific gravity roughly 2.8–3.0.
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Physical properties
Dark gray to rusty brown, fine-grained, rough, and locally vesicular with weathering cavities; typically dull to weakly lustered. Hardness about 5–6 Mohs, no obvious cleavage, and specific gravity roughly 2.8–3.0.
Formation & geological history
An extrusive volcanic rock formed when mafic lava cooled rapidly at or near the surface, likely during the Cenozoic or younger, though the image cannot establish age. The brown coloration and cavities reflect oxidation and weathering.
Uses & applications
Used as crushed aggregate, road stone, riprap, building stone, and occasionally as landscaping or lapidary material; this weathered specimen has limited jewelry value.
Geological facts
Its holes may be vesicles formed by gas bubbles in lava; some cavities can later be filled with zeolite, calcite, or quartz. The irregular surface is consistent with substantial chemical weathering.
Field identification & locations
Common in volcanic regions worldwide, including Hawaii, Iceland, the Pacific Northwest, India, and oceanic crust. Confirm with a fresh broken surface, dark fine grain, hardness near window glass, and lack of strong acid reaction; a magnet may show weak attraction if iron-rich.
