igneous
Dark river pebble (likely basalt or andesite)
Fine-grained basaltic or andesitic volcanic rock; exact identification is not possible from the image alone
AI-generated identification · may be incorrectSmall, rounded, dark gray-green pebble with a dull to slightly waxy surface and no visible crystals. If basaltic, typical minerals include plagioclase, pyroxene, and possibly olivine; hardness is roughly 5–6 Mohs.
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Physical properties
Small, rounded, dark gray-green pebble with a dull to slightly waxy surface and no visible crystals. If basaltic, typical minerals include plagioclase, pyroxene, and possibly olivine; hardness is roughly 5–6 Mohs.
Formation & geological history
Likely formed when lava cooled rapidly at or near Earth’s surface, then was rounded by water or abrasion. Its geological age and exact formation environment cannot be determined visually.
Uses & applications
Commonly collected as a natural pebble or used decoratively; this specimen is too small to assess for construction or industrial use.
Geological facts
Dark fine-grained volcanic rocks can look similar in photographs; a fresh broken surface and mineral or laboratory tests would help distinguish basalt from andesite.
Field identification & locations
Rounded edges, dark color, and fine texture suggest a water-worn volcanic pebble. Basalt and andesite occur worldwide, especially near volcanic regions and in river and beach deposits.
