igneous
Dark river-worn pebble, likely basalt
Basalt (fine-grained mafic volcanic rock; identification from the image is approximate)
AI-generated identification · may be incorrectSmooth, rounded, dark gray-green surface with a dull to slightly waxy luster; likely a mixture of plagioclase, pyroxene, and possibly olivine. Basalt’s constituent minerals are typically Mohs 5–6; the rock has no visible cleavage and a fine-grained texture.
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Physical properties
Smooth, rounded, dark gray-green surface with a dull to slightly waxy luster; likely a mixture of plagioclase, pyroxene, and possibly olivine. Basalt’s constituent minerals are typically Mohs 5–6; the rock has no visible cleavage and a fine-grained texture.
Formation & geological history
Basalt forms when iron- and magnesium-rich lava cools rapidly at or near the surface. Its age and original setting cannot be determined from the photograph; rounding suggests transport by water or abrasion.
Uses & applications
Basalt is widely used as crushed aggregate, road stone, and building material; this small pebble is mainly decorative or collectible.
Geological facts
Basalt is among Earth’s most abundant volcanic rocks and forms much of the ocean floor.
Field identification & locations
A dark, dense pebble with a fine-grained, non-layered interior is consistent with basalt; a fresh broken surface would help confirm it. Basalt is common in volcanic regions and river deposits; the image alone cannot rule out other dark rocks.
