igneous
Possible basalt pebble
Fine-grained mafic volcanic rock, commonly basalt (plagioclase, pyroxene, minor olivine/iron oxides)
AI-generated identification · may be incorrectDark gray-brown, rounded and weathered, with a dull earthy luster and fine-grained texture; typical hardness is about 5–6 Mohs, with no visible cleavage. The apparent hole may be a natural vesicle or weathering cavity, though its smoothness could indicate drilling or abrasion.
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Physical properties
Dark gray-brown, rounded and weathered, with a dull earthy luster and fine-grained texture; typical hardness is about 5–6 Mohs, with no visible cleavage. The apparent hole may be a natural vesicle or weathering cavity, though its smoothness could indicate drilling or abrasion.
Formation & geological history
Basalt 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. Its age cannot be determined from the photograph.
Uses & applications
Common basalt is used as aggregate, road stone, ballast, and dimension stone; small rounded pieces are collected but usually have little commercial value.
Geological facts
The specimen’s compact, oval shape and tiny cavity are consistent with a water-worn volcanic pebble, but the image cannot rule out slag, a drilled stone, or another dark fine-grained rock.
Field identification & locations
Look for a dense, matte dark rock with tiny crystals, high weight, and no glassy bubbles; basalt generally does not scratch easily with a steel nail. Common worldwide, especially near volcanic regions, beaches, and stream gravels.
