igneous
Rounded dark river pebble
Likely basalt or fine-grained andesite; exact identification requires testing
AI-generated identification · may be incorrectDark gray-green, fine-grained, dull to weakly silky luster, and smoothly water-worn; likely Mohs hardness 5–6.5, with no visible cleavage or crystals and moderate-to-high density.
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Physical properties
Dark gray-green, fine-grained, dull to weakly silky luster, and smoothly water-worn; likely Mohs hardness 5–6.5, with no visible cleavage or crystals and moderate-to-high density.
Formation & geological history
Probably an eroded volcanic rock transported and rounded by a stream, river, or beach; its age cannot be determined from the photograph and may range from recent to hundreds of millions of years.
Uses & applications
Suitable as a decorative pebble, landscaping stone, paperweight, or craft material; it has little commercial value unless unusually attractive or locally significant.
Geological facts
Basalt commonly contains microscopic plagioclase and pyroxene crystals, making it appear uniformly dark and dense. The greenish cast may reflect alteration minerals such as chlorite.
Field identification & locations
Look for a dense, nonporous, dark fine-grained surface; basalt generally does not fizz with dilute hydrochloric acid and may attract a weak magnet if iron-rich. Common in volcanic regions and stream gravels worldwide.
