igneous
Vesicular basalt (possibly amygdaloidal basalt)
Basalt; primarily plagioclase feldspar, pyroxene, and commonly olivine, with possible secondary zeolite or calcite fillings
AI-generated identification · may be incorrectDark gray, fine-grained volcanic rock with abundant rounded gas vesicles and a dull to weakly vitreous luster; hardness about 5–6, no obvious cleavage, and specific gravity roughly 2.7–3.0. The pinkish material may be a mineral-filled vesicle or a surface inclusion.
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Physical properties
Dark gray, fine-grained volcanic rock with abundant rounded gas vesicles and a dull to weakly vitreous luster; hardness about 5–6, no obvious cleavage, and specific gravity roughly 2.7–3.0. The pinkish material may be a mineral-filled vesicle or a surface inclusion.
Formation & geological history
Formed when basaltic lava cooled rapidly at or near Earth’s surface, trapping bubbles; typically Cenozoic to Recent, though basalt occurs throughout geologic time. Common in volcanic fields, lava flows, and oceanic crust.
Uses & applications
Used as aggregate, road base, riprap, railway ballast, and decorative stone; attractive amygdaloidal pieces may be collected or cut as lapidary specimens.
Geological facts
Vesicles record dissolved gases escaping from lava; later fluids can deposit colorful minerals such as calcite, quartz, chalcedony, or zeolites in the cavities.
Field identification & locations
Identify by its dark color, relatively low density, rough vesicular texture, and lack of visible large crystals; a streak test is usually gray, and it should not fizz strongly with dilute acid unless calcite is present. Common worldwide, especially Hawaii, Iceland, the Pacific Northwest, India, and oceanic islands.
