igneous
Tumbled basalt pebble
Basalt; fine-grained plagioclase feldspar and pyroxene, commonly with olivine and iron oxides
AI-generated identification · may be incorrectDark gray-green to brown, with a smooth polished surface and scattered lighter or darker grains. Typically Mohs 6; fine-grained, massive, and without visible cleavage; exact mineral proportions cannot be confirmed from the photo.
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Physical properties
Dark gray-green to brown, with a smooth polished surface and scattered lighter or darker grains. Typically Mohs 6; fine-grained, massive, and without visible cleavage; exact mineral proportions cannot be confirmed from the photo.
Formation & geological history
Basalt forms when mafic lava cools quickly at or near the surface. Basalt occurs from ancient to modern volcanic settings; the specimen’s age and source cannot be determined visually.
Uses & applications
Used as crushed aggregate, road stone, and building material; polished pebbles are sold for crafts and collecting.
Geological facts
Basalt is one of Earth’s most widespread volcanic rocks and makes up much of the oceanic crust.
Field identification & locations
The rounded shape and glossy finish indicate tumbling or water wear, not a natural crystal habit. Basalt is common in volcanic regions and river or beach gravels; confirm with a fresh surface and mineralogical testing.
