igneous
Vesicular basalt pebble with pale mineral infill
Basalt, likely amygdaloidal basalt; infill may be calcite, zeolite, or quartz
AI-generated identification · may be incorrectDark gray, fine-grained volcanic rock with rounded vesicles and contrasting white/tan fillings; typically dull to subtly glassy, hardness about 5–6, with no obvious cleavage. The smooth shape indicates water abrasion or tumbling.
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Physical properties
Dark gray, fine-grained volcanic rock with rounded vesicles and contrasting white/tan fillings; typically dull to subtly glassy, hardness about 5–6, with no obvious cleavage. The smooth shape indicates water abrasion or tumbling.
Formation & geological history
Formed when basaltic lava cooled rapidly at or near Earth’s surface, trapping gas bubbles later filled by circulating mineral-rich fluids. The basalt may be Cenozoic or older; age cannot be determined visually.
Uses & applications
Commonly used as aggregate, road stone, landscaping material, and decorative pebble; attractive amygdules increase collector interest but it is not typically a gemstone.
Geological facts
Vesicles distinguish it from most massive igneous rocks, while mineral-filled vesicles are called amygdules. A vinegar or dilute acid test may fizz if the white material is calcite.
Field identification & locations
Common near volcanic terrains and basalt shorelines, including the Pacific Northwest, Iceland, India, and Hawaii. Identify by its dense dark matrix, tiny cavities, and pale contrasting infill; a steel nail usually does not scratch fresh basalt.
