igneous
Rounded dark river stone, likely basalt
Basalt (fine-grained mafic volcanic rock; identification is provisional from the photo)
AI-generated identification · may be incorrectDark gray to black, dull to slightly waxy, with a fine-grained appearance and rounded, water-worn shape. Basalt is typically Mohs 6; individual crystals are too small to see, and the stone has no obvious cleavage.
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Physical properties
Dark gray to black, dull to slightly waxy, with a fine-grained appearance and rounded, water-worn shape. Basalt is typically Mohs 6; individual crystals are too small to see, and the stone has no obvious cleavage.
Formation & geological history
Basalt forms when iron- and magnesium-rich lava cools quickly at or near Earth’s surface; its age depends on its source. The smooth shape likely developed through abrasion during transport by water.
Uses & applications
Commonly used as aggregate, paving stone, and construction material; rounded examples are often kept as decorative or teaching specimens.
Geological facts
Basalt is among Earth’s most widespread volcanic rocks and forms much of the ocean floor.
Field identification & locations
A dark, dense-looking, fine-grained stone with no visible layering is consistent with basalt, but the image cannot confirm composition; a streak, fresh break, and hardness test can help. Basalt occurs worldwide, especially in volcanic regions and river or beach gravels.
