igneous
Vesicular basalt (likely weathered lava rock)
Vesicular basalt; primarily plagioclase feldspar, pyroxene, and volcanic glass, with possible iron-oxide alteration
AI-generated identification · may be incorrectDark gray, fine-grained, highly vesicular, with dull to slightly vitreous surfaces; hardness about 5–6 Mohs, no obvious cleavage, and moderate-to-high density except where pores are abundant. The rounded shape and pits may reflect weathering or abrasion.
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Physical properties
Dark gray, fine-grained, highly vesicular, with dull to slightly vitreous surfaces; hardness about 5–6 Mohs, no obvious cleavage, and moderate-to-high density except where pores are abundant. The rounded shape and pits may reflect weathering or abrasion.
Formation & geological history
Formed when basaltic lava cooled rapidly, trapping gas bubbles as vesicles; likely Cenozoic or younger, though age cannot be determined visually. Common in volcanic fields, lava flows, cinder deposits, and beach or stream gravels.
Uses & applications
Used as crushed aggregate, road base, landscaping stone, lightweight aggregate, and occasionally as a rough decorative specimen. It is generally not a jewelry gemstone.
Geological facts
Vesicles distinguish it from many dense basalts; mineral-filled vesicles would make it amygdaloidal basalt. The blue-gray coating may be weathering, staining, or surface residue rather than a primary mineral.
Field identification & locations
Identify by its dark fine-grained matrix, irregular gas cavities, heavy feel, and lack of visible large crystals; test with a steel file and inspect a fresh broken surface. Common worldwide in volcanic regions, including Hawaii, Iceland, the Pacific Northwest, and the Mediterranean.
