igneous
Rounded river pebble, likely dark basalt or andesite
Fine-grained mafic volcanic rock; exact identification is not possible from the photograph alone
AI-generated identification · may be incorrectDark gray-brown, rounded and dull, with a fine-grained appearance. Likely hardness around 5–6 Mohs; individual crystals and cleavage are not visible.
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Physical properties
Dark gray-brown, rounded and dull, with a fine-grained appearance. Likely hardness around 5–6 Mohs; individual crystals and cleavage are not visible.
Formation & geological history
Probably formed when lava cooled at or near Earth’s surface, then became rounded by transport in water. Its age and specific formation environment cannot be determined from appearance alone.
Uses & applications
Commonly collected as a natural pebble or used decoratively in landscaping; it has no clear gemstone or industrial value as a single specimen.
Geological facts
The smooth shape is consistent with abrasion during transport, though the pebble may also have been naturally weathered in place.
Field identification & locations
Look for a dense, fine-grained texture and lack of visible layering or large crystals; a fresh broken surface, streak, and hardness test would help distinguish basalt from other dark rocks. Dark volcanic pebbles occur in many river and coastal settings.
