igneous
Vesicular basalt (scoriaceous volcanic rock)
Basalt, chiefly plagioclase, pyroxene, and commonly olivine; vesicles may be lined with secondary minerals
AI-generated identification · may be incorrectHardness about 5–6 Mohs; pale gray-green to tan, dull to slightly earthy luster, fine-grained groundmass with abundant rounded gas cavities. Generally massive with no cleavage; specific gravity commonly 2.4–2.9, reduced by vesicles.
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Physical properties
Hardness about 5–6 Mohs; pale gray-green to tan, dull to slightly earthy luster, fine-grained groundmass with abundant rounded gas cavities. Generally massive with no cleavage; specific gravity commonly 2.4–2.9, reduced by vesicles.
Formation & geological history
Formed when basaltic lava erupted and cooled rapidly at or near Earth’s surface, trapping gas bubbles; the pale coating may reflect weathering or alteration. Basalt ranges from Precambrian to modern, depending on locality.
Uses & applications
Used as lightweight aggregate, road material, landscaping stone, and occasionally abrasive or decorative material; ordinary specimens have little jewelry value.
Geological facts
Vesicles distinguish it from dense basalt, while irregular cavities and a rough surface distinguish it from pumice, which is usually much lighter and more highly porous.
Field identification & locations
Common in volcanic regions, including Hawaii, Iceland, the Pacific Northwest, oceanic islands, and mid-ocean ridges. A fresh broken surface, dark fine-grained matrix, magnetic response, and density greater than water support identification; exact classification needs petrographic or chemical testing.
