igneous
Rounded gray-green river pebble, likely basalt or andesite
Fine-grained mafic volcanic rock; exact identification requires closer examination
AI-generated identification · may be incorrectSmooth, water-worn surface; gray-green with tiny pale grains. Likely Mohs hardness 5–6, dull to weakly lustrous, fine-grained crystalline texture, and no visible cleavage; density is probably around 2.7–3.0 g/cm³.
Identified More igneous →
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Physical properties
Smooth, water-worn surface; gray-green with tiny pale grains. Likely Mohs hardness 5–6, dull to weakly lustrous, fine-grained crystalline texture, and no visible cleavage; density is probably around 2.7–3.0 g/cm³.
Formation & geological history
If volcanic, it formed when lava cooled rapidly at or near Earth’s surface, then was rounded by stream or shoreline abrasion. Its geological age and precise source cannot be determined from the photograph.
Uses & applications
Primarily a natural decorative or collecting pebble; comparable volcanic rock is also used as aggregate and paving stone.
Geological facts
The rounded shape indicates prolonged abrasion, but color and texture alone cannot reliably distinguish basalt from andesite or other dark, fine-grained rocks.
Field identification & locations
Look for a dense, fine-grained interior and, in basalt, possible tiny vesicles or crystals; a fresh broken surface or simple tests would improve identification. Volcanic pebbles occur in river and beach gravels worldwide.
