igneous
Rounded vesicular basalt cobble
Basalt, a fine-grained volcanic rock composed mainly of plagioclase, pyroxene, and commonly olivine
AI-generated identification · may be incorrectDark gray to black, matte surface with small pits or vesicles; typically Mohs hardness 5–6, fine-grained/interlocking crystals, and no visible cleavage. The rounded shape and surface suggest water-worn basalt, though the image alone cannot confirm its identity.
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Physical properties
Dark gray to black, matte surface with small pits or vesicles; typically Mohs hardness 5–6, fine-grained/interlocking crystals, and no visible cleavage. The rounded shape and surface suggest water-worn basalt, though the image alone cannot confirm its identity.
Formation & geological history
Basalt forms when low-silica lava cools at or near Earth’s surface; its age varies widely, from recent volcanic flows to ancient rocks. Vesicles form as gas escapes from cooling lava, and rounding commonly results from transport in water.
Uses & applications
Commonly used as crushed aggregate, road stone, and construction material; rounded specimens are mainly decorative or collectible.
Geological facts
Basalt is among Earth’s most abundant volcanic rocks and also makes up much of the oceanic crust.
Field identification & locations
Look for a dense, dark, fine-grained rock, sometimes with gas-bubble pits; basalt is widespread in volcanic regions and river or beach gravels. Confirming it requires closer examination, since other dark stones can look similar.
