igneous
Vesicular basalt
Basalt; fine-grained mafic volcanic rock, chiefly plagioclase, pyroxene, and commonly olivine
AI-generated identification · may be incorrectDark gray to black, fine-grained, dull to slightly vitreous, with small gas vesicles and weathered pale mineral patches. Hardness about 6 on Mohs scale; no obvious cleavage; typically dense, though vesicles reduce specific gravity to roughly 2.4–3.0.
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Physical properties
Dark gray to black, fine-grained, dull to slightly vitreous, with small gas vesicles and weathered pale mineral patches. Hardness about 6 on Mohs scale; no obvious cleavage; typically dense, though vesicles reduce specific gravity to roughly 2.4–3.0.
Formation & geological history
Forms when iron- and magnesium-rich lava cools rapidly at or near Earth’s surface, commonly in volcanic flows. Most examples are geologically young relative to continental rocks, ranging from recent eruptions to Precambrian formations.
Uses & applications
Used as crushed aggregate, road base, riprap, railroad ballast, building stone, and occasionally landscaping material; ordinary specimens have little jewelry value.
Geological facts
The holes are gas bubbles trapped during cooling, distinguishing vesicular basalt from many intrusive rocks. Pale patches may be plagioclase, zeolite, calcite, or weathering products; the apparent white streak could also be an applied residue or vein.
Field identification & locations
Common in volcanic regions, oceanic crust, Hawaii, Iceland, the Columbia River Basalt Province, and many continental lava fields. Field identification relies on its dark color, fine texture, strong weight, and vesicles; a streak is usually gray, and it is generally nonmagnetic to weakly magnetic.
