igneous
Rounded dark river pebble
Likely basalt or fine-grained andesite; exact identification requires testing
AI-generated identification · may be incorrectDark gray-green, smooth and water-rounded, with a dull to slightly waxy luster and fine-grained texture; typically hardness 5–6 Mohs, no visible cleavage, and specific gravity about 2.7–3.0.
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Physical properties
Dark gray-green, smooth and water-rounded, with a dull to slightly waxy luster and fine-grained texture; typically hardness 5–6 Mohs, no visible cleavage, and specific gravity about 2.7–3.0.
Formation & geological history
Likely a weathered volcanic rock fragment transported and rounded by a stream, beach, or glacial environment. Its precise geological age cannot be determined from the photograph.
Uses & applications
Commonly used as landscaping or decorative stone, craft material, and aquarium gravel; this small pebble has little commercial value.
Geological facts
Basalt is composed mainly of plagioclase feldspar and pyroxene, sometimes with olivine or magnetite. Its dark color reflects rapid cooling of iron- and magnesium-rich lava.
Field identification & locations
Identify it by its uniform fine grain, dark color, heft, and lack of layering; a streak test, magnet test, hardness test, and fresh broken surface would help distinguish basalt from shale or slag. Common in volcanic regions and river gravels worldwide.
