igneous
Vesicular basalt (scoria-like lava rock)
Vesicular basalt; chiefly plagioclase, pyroxene, olivine, and volcanic glass
AI-generated identification · may be incorrectDark gray, highly vesicular, rough, and dull to slightly glassy; typically hardness 5–6, no obvious cleavage, fine-grained matrix, and specific gravity about 2.2–2.9 depending on pore volume. The numerous rounded holes formed from trapped gas bubbles.
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Physical properties
Dark gray, highly vesicular, rough, and dull to slightly glassy; typically hardness 5–6, no obvious cleavage, fine-grained matrix, and specific gravity about 2.2–2.9 depending on pore volume. The numerous rounded holes formed from trapped gas bubbles.
Formation & geological history
An extrusive igneous rock formed when basaltic lava cooled rapidly at or near the surface, commonly during a late, gas-rich phase of an eruption. Its exact geological age cannot be determined from the image; it may range from recent volcanic material to ancient basalt.
Uses & applications
Used as lightweight aggregate, landscaping stone, drainage material, erosion control, and occasionally in decorative masonry. It has limited jewelry value but is popular as a distinctive collector or garden specimen.
Geological facts
The large cavities are vesicles, sometimes later lined or filled by minerals such as calcite, zeolites, or quartz. Extremely porous pieces may be scoria; gray, denser specimens are generally called vesicular basalt.
Field identification & locations
Identify it by its volcanic texture, abundant interconnected vesicles, gray-black color, and relatively light weight; it should not fizz with dilute acid unless carbonate minerals fill the cavities. Common worldwide in basaltic volcanic regions, including Hawaii, Iceland, Mexico, and the western United States.
