igneous
Dark rounded pebble
Likely basalt or another fine-grained mafic volcanic rock; exact identification is uncertain from the image
AI-generated identification · may be incorrectDark gray-brown, dull to slightly earthy luster, fine-grained and rounded by weathering or transport; basalt typically has Mohs hardness 5–6, no visible cleavage, and specific gravity about 2.8–3.0.
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Physical properties
Dark gray-brown, dull to slightly earthy luster, fine-grained and rounded by weathering or transport; basalt typically has Mohs hardness 5–6, no visible cleavage, and specific gravity about 2.8–3.0.
Formation & geological history
Likely formed when mafic lava cooled rapidly at or near Earth’s surface, then became rounded through erosion; its precise geological age and setting cannot be determined visually.
Uses & applications
Common basalt is used as aggregate, paving stone, ballast, and building material; an ordinary pebble has little jewelry or collector use.
Geological facts
The specimen appears only a few centimeters across and may also be a weathered sedimentary or metamorphic pebble; lighting and low resolution obscure texture and mineral grains.
Field identification & locations
Field clues favor basalt if it is uniformly dark, dense, fine-grained, and leaves a gray streak; check for vesicles, tiny crystals, magnetic response, and hardness. Common worldwide, especially near volcanic terrain and streambeds.
