igneous
Likely basalt pebble
Basalt, a fine-grained mafic volcanic rock; commonly composed of plagioclase, pyroxene, and sometimes olivine
AI-generated identification · may be incorrectDark gray to black, matte to faintly subvitreous, fine-grained, and rounded from abrasion; hardness is roughly 5–6 Mohs, with no visible cleavage and typically high density (~2.8–3.0 g/cm³). The image alone cannot confirm mineralogy or rule out slag or another dark stone.
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Physical properties
Dark gray to black, matte to faintly subvitreous, fine-grained, and rounded from abrasion; hardness is roughly 5–6 Mohs, with no visible cleavage and typically high density (~2.8–3.0 g/cm³). The image alone cannot confirm mineralogy or rule out slag or another dark stone.
Formation & geological history
Forms when iron- and magnesium-rich lava rapidly cools at or near Earth’s surface, commonly in oceanic crust, volcanic fields, and ancient lava flows; specimens may range from recent to billions of years old.
Uses & applications
Used extensively as crushed aggregate, road base, railroad ballast, riprap, and building stone; attractive polished pieces are occasionally sold as curios or lapidary material.
Geological facts
Basalt is Earth’s most abundant volcanic rock and makes up much of the ocean floor. Vesicles, if present, indicate gas bubbles in the cooling lava, but none are obvious here.
Field identification & locations
Look for a uniformly fine texture, black color, heavy feel, and occasional tiny pale plagioclase crystals; a streak, magnet test, and specific-gravity measurement help distinguish basalt from industrial slag or meteorite material.
