igneous
Vesicular basalt (weathered volcanic rock)
Basalt, chiefly plagioclase feldspar, clinopyroxene, and possibly olivine/iron oxides
AI-generated identification · may be incorrectTypically dark gray to brown, fine-grained, matte to slightly earthy, with abundant weathering pits and vesicles; hardness about 5–6 Mohs, massive texture, and no prominent cleavage. The dark central material may be fresher basalt or an iron-rich weathering zone.
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Physical properties
Typically dark gray to brown, fine-grained, matte to slightly earthy, with abundant weathering pits and vesicles; hardness about 5–6 Mohs, massive texture, and no prominent cleavage. The dark central material may be fresher basalt or an iron-rich weathering zone.
Formation & geological history
Forms when low-silica lava cools rapidly at or near Earth’s surface, commonly in volcanic flows; vesicles are gas bubbles preserved during cooling. The specimen is likely geologically young compared with continental rocks, though its exact age and locality cannot be determined visually.
Uses & applications
Used as crushed aggregate, road base, railroad ballast, riprap, and occasionally building or landscaping stone; attractive polished pieces may be collected but it is not generally a gemstone.
Geological facts
Basalt is the most abundant volcanic rock on oceanic crust and commonly forms shield volcanoes, lava plateaus, and mid-ocean ridges.
Field identification & locations
Identify it by its dense fine grain, dark color, irregular vesicles, and lack of visible quartz or large crystals; common worldwide, especially Hawaii, Iceland, India’s Deccan Traps, and oceanic islands. A streak, magnetism, thin-section, or chemical test would help distinguish basalt from weathered scoria or slag.
