igneous
Weathered vesicular basalt (scoriaceous basalt)
Basalt, predominantly plagioclase + pyroxene ± olivine; vesicular variety
AI-generated identification · may be incorrectDark brown to black, strongly weathered, rough and porous with irregular vesicles; dull to slightly earthy luster and fine-grained crystalline texture. Hardness about 5–6 Mohs; no obvious cleavage; specific gravity commonly 2.7–3.0, reduced by vesicles.
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Physical properties
Dark brown to black, strongly weathered, rough and porous with irregular vesicles; dull to slightly earthy luster and fine-grained crystalline texture. Hardness about 5–6 Mohs; no obvious cleavage; specific gravity commonly 2.7–3.0, reduced by vesicles.
Formation & geological history
An extrusive mafic igneous rock formed when basaltic lava cooled rapidly at or near Earth’s surface, with gas bubbles producing vesicles; the brown coloration reflects oxidation and weathering. Basalt forms from Precambrian to modern ages in volcanic fields, mid-ocean ridges, and oceanic islands.
Uses & applications
Used as crushed aggregate, road base, riprap, and occasionally dimension stone; vesicular pieces are mainly educational or decorative specimens rather than jewelry material.
Geological facts
Basalt is the most abundant volcanic rock on Earth and makes up much of the oceanic crust. Vesicle-rich basalt may grade into scoria, but scoria is typically lighter, more extremely porous, and commonly reddish.
Field identification & locations
Identify it by its dark mafic color, fine texture, heavy feel, and gas cavities; a streak test is usually grayish-black, and it is not attracted to a magnet unless magnetite-rich. Common worldwide in volcanic regions, including Hawaii, Iceland, India, and the western United States.
