igneous
Likely basalt (possibly fine-grained gabbro)
Basalt; predominantly plagioclase feldspar, pyroxene, and commonly olivine
AI-generated identification · may be incorrectDark gray-black, fine-grained, massive, and dull to faintly submetallic where polished or freshly broken; Mohs hardness about 5–6, with no obvious cleavage and typical specific gravity 2.8–3.0. The rounded form and smooth facets suggest a naturally worn or human-shaped piece.
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Physical properties
Dark gray-black, fine-grained, massive, and dull to faintly submetallic where polished or freshly broken; Mohs hardness about 5–6, with no obvious cleavage and typical specific gravity 2.8–3.0. The rounded form and smooth facets suggest a naturally worn or human-shaped piece.
Formation & geological history
An extrusive mafic igneous rock formed when iron- and magnesium-rich lava cooled rapidly at or near Earth’s surface, commonly during volcanic eruptions or ocean-floor spreading. Basalt ranges from modern to Precambrian in age.
Uses & applications
Widely used as crushed aggregate, roadstone, railroad ballast, riprap, building stone, and mineral wool; attractive polished pieces are used decoratively and as specimens. Common material generally has modest commercial value.
Geological facts
Basalt is the most abundant volcanic rock on Earth and forms much of the oceanic crust. The image alone cannot distinguish it confidently from dark fine-grained gabbro, diabase, or another mafic rock.
Field identification & locations
Look for a uniformly dark, fine texture, high density, and lack of visible large crystals; a streak is usually gray, and it is generally nonmagnetic or only weakly magnetic. Common worldwide, especially Hawaii, Iceland, India’s Deccan Traps, and oceanic terrains.
