igneous
Dark volcanic rock, likely basalt
Basalt; chiefly plagioclase feldspar, pyroxene, and commonly olivine or iron oxides
AI-generated identification · may be incorrectFine-grained, black to dark gray, generally dull to subtly glassy, with hardness about 5–6 Mohs and specific gravity roughly 2.8–3.0. The specimen appears vesicular or irregularly weathered, but details are limited by the image.
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Physical properties
Fine-grained, black to dark gray, generally dull to subtly glassy, with hardness about 5–6 Mohs and specific gravity roughly 2.8–3.0. The specimen appears vesicular or irregularly weathered, but details are limited by the image.
Formation & geological history
Basalt forms when low-viscosity mafic lava rapidly cools at or near Earth’s surface; it commonly ranges from recent eruptions to Archean volcanic rocks over 4 billion years old.
Uses & applications
Widely used as crushed aggregate, road base, railroad ballast, riprap, and building stone; attractive polished varieties are used decoratively, but this small fragment has little commercial value.
Geological facts
Basalt is the most abundant volcanic rock and makes up much of oceanic crust. Its dark color reflects abundant ferromagnesian minerals and iron-rich oxides.
Field identification & locations
Identify it by its dark color, fine texture, heavy feel, and lack of visible large crystals; a streak test, magnetism check, and hand lens would help distinguish basalt from slag or other dark rocks. Common worldwide, especially volcanic regions and ocean-floor exposures.
