igneous
Rounded river pebble (likely weathered basalt or andesite)
Fine-grained mafic to intermediate volcanic rock; exact identification requires testing
AI-generated identification · may be incorrectDark gray-brown, rounded and smoothly weathered, with a dull to faintly subvitreous luster and no visible crystals. Likely Mohs hardness 5–6, specific gravity about 2.7–3.0; massive, with indistinct cleavage.
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Physical properties
Dark gray-brown, rounded and smoothly weathered, with a dull to faintly subvitreous luster and no visible crystals. Likely Mohs hardness 5–6, specific gravity about 2.7–3.0; massive, with indistinct cleavage.
Formation & geological history
Formed from ancient volcanic lava, then transported and abrasion-rounded by water or sediment. Its geological age cannot be determined from the photograph and may range from recent surface material to millions of years old.
Uses & applications
Commonly used as landscaping stone, aquarium décor, aggregate, or a teaching specimen; little jewelry value unless unusually patterned or polished.
Geological facts
The mottled tan-gray surface may reflect weathering, iron staining, or lichen rather than the rock’s fresh interior.
Field identification & locations
Look for a fine-grained, dense interior and a streak that is usually pale gray; a magnet may show weak attraction if magnetite is present. Basaltic pebbles are widespread in stream gravels and volcanic regions.
