igneous
Likely basalt or basaltic scoria
Mafic volcanic rock, chiefly plagioclase and pyroxene, commonly with olivine; approximate composition: ~45–52% SiO₂
AI-generated identification · may be incorrectDark gray to black, fine-grained and massive, with dull to weakly vitreous luster and irregular fracture. Basalt is typically Mohs 5–6; the pieces may contain vesicles, though this image does not show enough detail to confirm them.
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Physical properties
Dark gray to black, fine-grained and massive, with dull to weakly vitreous luster and irregular fracture. Basalt is typically Mohs 5–6; the pieces may contain vesicles, though this image does not show enough detail to confirm them.
Formation & geological history
Formed when iron- and magnesium-rich lava cooled rapidly at or near Earth’s surface, commonly during Quaternary or older volcanic eruptions. Exact age and locality cannot be determined photographically.
Uses & applications
Used as crushed aggregate, road base, riprap, railway ballast, and building stone; attractive polished basalt is occasionally used decoratively. Common specimens generally have little commercial value.
Geological facts
The pieces appear to be natural, angular volcanic fragments rather than a single identifiable crystal or gemstone. Their very dark appearance could also reflect weathering or lighting.
Field identification & locations
Common worldwide in volcanic regions, including Hawaii, Iceland, India, the Pacific Northwest, and oceanic crust. A fresh broken surface, fine texture, high density, and lack of visible individual crystals support basalt; a magnet and streak test can provide additional clues.
