igneous
Smooth dark river pebble
Likely basalt or fine-grained mafic volcanic rock; exact identification requires testing
AI-generated identification · may be incorrectDark gray-green, fine-grained, opaque, and weakly lustered with a rounded, water-worn surface; basalt typically has Mohs hardness 5–6, no visible cleavage, and specific gravity about 2.8–3.1.
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Physical properties
Dark gray-green, fine-grained, opaque, and weakly lustered with a rounded, water-worn surface; basalt typically has Mohs hardness 5–6, no visible cleavage, and specific gravity about 2.8–3.1.
Formation & geological history
Likely formed from rapidly cooled mafic lava, then rounded by stream or beach transport; its geological age cannot be determined from the photograph and may range from recent to ancient.
Uses & applications
Used as a decorative pebble, massage stone, landscaping aggregate, or craft material; not generally valuable as jewelry unless unusually patterned or polished.
Geological facts
The subtle green tone may reflect chlorite, olivine alteration, or weathering. A dense, uniformly fine texture and lack of visible quartz or large crystals are consistent with basalt.
Field identification & locations
Common in volcanic terrains and river gravels worldwide. Check for a fine crystalline texture, heavy feel, nonmetallic streak, and hardness sufficient to scratch glass; a magnet test may show weak attraction if magnetite is present.
