igneous
Rounded river pebble, likely basalt or weathered andesite
Fine-grained mafic volcanic rock; exact identification requires testing or microscopy
AI-generated identification · may be incorrectDark gray-brown, smooth and water-worn, with dull to slightly subvitreous luster and no visible crystals. Likely hardness 5.5–6.5 Mohs; massive texture, negligible cleavage, and specific gravity roughly 2.7–3.1.
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Physical properties
Dark gray-brown, smooth and water-worn, with dull to slightly subvitreous luster and no visible crystals. Likely hardness 5.5–6.5 Mohs; massive texture, negligible cleavage, and specific gravity roughly 2.7–3.1.
Formation & geological history
Probably formed from rapidly cooled lava, then rounded by stream or beach transport; its precise geological age cannot be determined from the image. Weathering has produced the brown surface staining.
Uses & applications
Common pebbles have little commercial value, though basalt is widely used as aggregate, paving stone, road base, and landscaping material. This individual specimen may be useful as a teaching or decorative stone.
Geological facts
The smooth, symmetrical shape indicates prolonged abrasion rather than crystal growth. Brown coloration commonly reflects oxidation of iron-bearing minerals.
Field identification & locations
Look for a uniformly fine-grained dark interior, weak magnetism, and no acid reaction; a fresh chip and streak, magnet, hardness, and density tests would distinguish basalt from andesite or other dark stones. Common in volcanic regions and gravel deposits.
