igneous
Rounded basaltic river pebble
Basalt, likely vesicular/amygdaloidal basalt
AI-generated identification · may be incorrectDark gray-brown, fine-grained, dull to faintly earthy luster, with small pits or vesicles and possible weathering stains. Hardness about 6–7 Mohs; composed mainly of plagioclase and pyroxene, with possible olivine or iron oxides; cleavage is not visible in the whole rock.
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Physical properties
Dark gray-brown, fine-grained, dull to faintly earthy luster, with small pits or vesicles and possible weathering stains. Hardness about 6–7 Mohs; composed mainly of plagioclase and pyroxene, with possible olivine or iron oxides; cleavage is not visible in the whole rock.
Formation & geological history
Basalt forms when low-silica lava rapidly cools at or near Earth’s surface, commonly in volcanic fields, oceanic crust, and flood-basalt provinces. This specimen was likely rounded by stream or beach abrasion; its exact geological age cannot be determined from the image.
Uses & applications
Used as crushed aggregate, road stone, railway ballast, riprap, and landscaping material; attractive pieces may be sold as curios or lapidary rough. It has little value unless unusually patterned, vesicular, or from a notable locality.
Geological facts
The rounded shape and pitted surface indicate prolonged transport and weathering rather than a fresh volcanic fragment. Some cavities may once have contained gas bubbles or later mineral fillings.
Field identification & locations
Identify by its heavy feel, fine texture, dark color, lack of visible quartz, and inability to scratch it with a steel knife easily. Common in volcanic terrains and downstream gravel beds; a hand lens and streak, magnetism, or thin-section test would improve identification.
