igneous
Vesicular basalt
Basalt, commonly composed of plagioclase, pyroxene, olivine, and volcanic glass
AI-generated identification · may be incorrectDark gray, fine-grained, and typically dull to slightly glassy; abundant rounded vesicles (gas cavities) are visible. Hardness is about 5–6 Mohs, with no obvious cleavage and specific gravity roughly 2.7–3.0.
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Physical properties
Dark gray, fine-grained, and typically dull to slightly glassy; abundant rounded vesicles (gas cavities) are visible. Hardness is about 5–6 Mohs, with no obvious cleavage and specific gravity roughly 2.7–3.0.
Formation & geological history
An extrusive igneous rock formed when iron- and magnesium-rich lava cooled rapidly at or near Earth’s surface, trapping volcanic gas bubbles. Most examples formed during relatively recent volcanic episodes, generally younger than 100 million years.
Uses & applications
Used as crushed aggregate, road base, riprap, landscaping stone, and occasionally architectural stone; porous pieces are mainly collected as volcanic specimens rather than used in jewelry.
Geological facts
The holes are vesicles, produced by expanding dissolved gases; if later filled with minerals, the rock is called amygdaloidal basalt. Its rounded exterior suggests natural weathering or stream/beach abrasion.
Field identification & locations
Identify it by its dark fine-grained matrix, high density, and abundant cavities; it is commonly found in lava flows, volcanic islands, oceanic crust, and basalt quarries. A magnet may show weak attraction from iron-bearing minerals.
