igneous
Vesicular basalt (lava rock)
Basalt, a mafic volcanic rock composed mainly of plagioclase feldspar, pyroxene, and commonly olivine
AI-generated identification · may be incorrectDark gray to black, fine-grained, highly vesicular, with dull to slightly glassy luster; hardness about 5–6 Mohs, no prominent cleavage, and typical specific gravity around 2.7–3.0. The abundant holes are gas bubbles preserved as vesicles.
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Physical properties
Dark gray to black, fine-grained, highly vesicular, with dull to slightly glassy luster; hardness about 5–6 Mohs, no prominent cleavage, and typical specific gravity around 2.7–3.0. The abundant holes are gas bubbles preserved as vesicles.
Formation & geological history
Formed when basaltic lava erupted and cooled rapidly at or near Earth’s surface; individual specimens may range from ancient volcanic flows to relatively recent lava. Common settings include shield volcanoes, oceanic crust, and cinder cones.
Uses & applications
Used as lightweight aggregate, landscaping stone, drainage material, abrasives, and occasionally decorative rock; generally little jewelry value.
Geological facts
Its low silica and high iron–magnesium content produce the dark color. Vesicles may later become filled with minerals such as zeolite, calcite, or quartz.
Field identification & locations
Identify by its dark color, fine texture, light weight for its size, and numerous irregular cavities; it is generally nonmagnetic or weakly magnetic. Common worldwide, especially Hawaii, Iceland, the Pacific Northwest, India, and volcanic regions.
