igneous
Polished black pebble, likely basalt
Basalt, a fine-grained mafic volcanic rock; identification is tentative from the image
AI-generated identification · may be incorrectDark gray to black, fine-grained, and polished with a subdued luster. Basalt is typically Mohs 6; individual crystals are too small to see, and the pebble’s specific gravity cannot be determined visually.
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Physical properties
Dark gray to black, fine-grained, and polished with a subdued luster. Basalt is typically Mohs 6; individual crystals are too small to see, and the pebble’s specific gravity cannot be determined visually.
Formation & geological history
Basalt forms when iron- and magnesium-rich lava cools rapidly at or near Earth’s surface. It occurs from ancient to recent volcanic settings; the specimen’s age and source are unknown.
Uses & applications
Polished basalt pebbles are used for decoration, jewelry, and crafts; crushed basalt is used as aggregate and road stone.
Geological facts
Basalt is one of Earth’s most widespread volcanic rocks and forms much of the ocean floor.
Field identification & locations
Its uniformly dark, fine-grained appearance is consistent with basalt, but other black rocks or minerals can look similar; a scratch or streak test and close inspection would help confirm it. Basalt is common in volcanic regions worldwide.
