igneous
Likely basalt or dark volcanic rock
Fine-grained mafic igneous rock, probably basalt; exact identification requires testing
AI-generated identification · may be incorrectDark gray to black, dull to weakly vitreous luster, irregular fracture, and apparently fine-grained texture; typical basalt hardness is about 6 Mohs and specific gravity 2.8–3.0. The image does not resolve crystals or vesicles.
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Physical properties
Dark gray to black, dull to weakly vitreous luster, irregular fracture, and apparently fine-grained texture; typical basalt hardness is about 6 Mohs and specific gravity 2.8–3.0. The image does not resolve crystals or vesicles.
Formation & geological history
Basalt forms when iron- and magnesium-rich lava rapidly cools at or near Earth’s surface, commonly in oceanic crust, lava flows, and volcanic islands; specimens may range from Precambrian to modern. This piece appears naturally broken or roughly cut.
Uses & applications
Used as crushed aggregate, road metal, construction stone, and occasionally ornamental rock; unexceptional fragments have little jewelry value.
Geological facts
Basalt is the most abundant volcanic rock and makes up much of the ocean floor. A magnetic response may occur because of magnetite.
Field identification & locations
Look for tiny interlocking crystals, possible vesicles, high density, and a strong streak-free appearance; distinguish it from slag by the absence of abundant glassy bubbles and from meteorite by lack of a fusion crust and metal. Common worldwide, especially volcanic regions.
