igneous
Likely basalt (possibly scoriaceous basalt)
Basalt; chiefly plagioclase feldspar, pyroxene, and commonly olivine, with minor iron–titanium oxides
AI-generated identification · may be incorrectDark gray-black, fine-grained to subtly vesicular, with a dull to weakly vitreous luster; hardness about 6–6.5 Mohs, no visible cleavage, and specific gravity roughly 2.8–3.0. The specimen appears rounded or naturally weathered, though its texture is partly obscured by the image.
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Physical properties
Dark gray-black, fine-grained to subtly vesicular, with a dull to weakly vitreous luster; hardness about 6–6.5 Mohs, no visible cleavage, and specific gravity roughly 2.8–3.0. The specimen appears rounded or naturally weathered, though its texture is partly obscured by the image.
Formation & geological history
Basalt forms when low-silica magma cools rapidly at or near Earth’s surface, commonly in lava flows, oceanic crust, and volcanic islands. Most examples are Cenozoic or younger, but basalt occurs throughout geological time.
Uses & applications
Used as crushed aggregate, roadstone, railroad ballast, riprap, and dimension stone; attractive polished pieces may be sold as decorative or teaching specimens.
Geological facts
Basalt is the most abundant volcanic rock and makes up much of the ocean floor. Vesicles indicate gas bubbles trapped during lava cooling; metallic flecks may be magnetite or other oxides.
Field identification & locations
Identify it by its dense dark color, fine grain, blocky fracture, and possible magnetic response; it should not fizz with dilute hydrochloric acid. Common locations include Hawaii, Iceland, India’s Deccan Traps, oceanic islands, and volcanic regions worldwide.
