igneous
Dark fine-grained rock, likely basalt
Basalt; primarily plagioclase feldspar, clinopyroxene, and commonly olivine or iron-titanium oxides
AI-generated identification · may be incorrectTypically black to dark gray, fine-grained, massive, and dull to slightly vitreous; hardness about 5–6, with no obvious cleavage and relatively high specific gravity (~2.8–3.0). The specimen appears granular and vesicle-free, though the image is insufficient for certainty.
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Physical properties
Typically black to dark gray, fine-grained, massive, and dull to slightly vitreous; hardness about 5–6, with no obvious cleavage and relatively high specific gravity (~2.8–3.0). The specimen appears granular and vesicle-free, though the image is insufficient for certainty.
Formation & geological history
Basalt forms when low-silica mafic lava rapidly cools at or near Earth’s surface, commonly in volcanic flows, oceanic crust, and hotspots. Most examples are geologically young, but basalt occurs from Archean terrains to modern eruptions.
Uses & applications
Used extensively as crushed aggregate, road base, railway ballast, dimension stone, and sometimes mineral wool; attractive polished pieces may be used decoratively, but this sample is not gem-quality.
Geological facts
Basalt is the most abundant volcanic rock and makes up much of the oceanic crust. Its dark color reflects abundant mafic minerals and iron-rich oxides.
Field identification & locations
Identify it by its dark color, fine interlocking texture, heavy feel, and lack of visible large crystals; a streak, hardness, and density test would help distinguish it from slag or other dark rocks. Common worldwide, especially volcanic regions and ocean-floor exposures.
