igneous
Vesicular basalt (possibly scoria)
Basalt; chiefly plagioclase feldspar, pyroxene, and often olivine, with volcanic glass
AI-generated identification · may be incorrectDark gray-green, fine-grained, dull to slightly vitreous, with abundant rounded vesicles and scattered pale crystals. Typically hardness 5–6, no obvious cleavage, massive texture, and specific gravity about 2.7–3.1; the relatively dense appearance suggests basalt rather than very porous scoria.
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Physical properties
Dark gray-green, fine-grained, dull to slightly vitreous, with abundant rounded vesicles and scattered pale crystals. Typically hardness 5–6, no obvious cleavage, massive texture, and specific gravity about 2.7–3.1; the relatively dense appearance suggests basalt rather than very porous scoria.
Formation & geological history
An extrusive mafic igneous rock formed when iron- and magnesium-rich lava cooled rapidly at or near Earth’s surface; vesicles formed from escaping gas bubbles. Its age cannot be determined from the photograph and may range from recent volcanic material to ancient basalt.
Uses & applications
Used as crushed aggregate, roadstone, railway ballast, riprap, and decorative stone; attractive vesicular pieces are collected, though this specimen appears ordinary rather than gem-quality.
Geological facts
Basalt is the most common volcanic rock and forms much of the oceanic crust. The holes are gas cavities, sometimes later filled by minerals such as calcite, zeolites, or quartz.
Field identification & locations
Identify it by its black fine-grained groundmass, heavy feel, mafic composition, and gas cavities; test for weak magnetism and inspect broken surfaces for tiny feldspar crystals. Common worldwide in volcanic regions, including Hawaii, Iceland, India, and oceanic islands.
