igneous
Rounded brown-gray pebble, likely weathered basalt or iron-stained chert
Indeterminate from image; possible basalt (plagioclase–pyroxene) or chert (microcrystalline SiO₂)
AI-generated identification · may be incorrectSmall, smooth, subrounded specimen with mottled brown-gray coloration and dull to slightly earthy luster. Basalt typically has Mohs hardness 5–6 and dense fine-grained texture; chert is harder, about 6.5–7, and may show a waxy luster.
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Physical properties
Small, smooth, subrounded specimen with mottled brown-gray coloration and dull to slightly earthy luster. Basalt typically has Mohs hardness 5–6 and dense fine-grained texture; chert is harder, about 6.5–7, and may show a waxy luster.
Formation & geological history
Likely naturally weathered from a stream, beach, or glacial deposit; its geological age and formation cannot be determined from the photograph. Brown areas may reflect oxidation of iron-bearing minerals.
Uses & applications
Common specimens have little commercial value and are mainly used for teaching or casual collecting; basalt is used as aggregate and building stone, while chert can be used for tools and decorative stone.
Geological facts
The rounded shape indicates abrasion during transport. A steel nail or knife may scratch softer basalt but should not scratch chert; streak and acid tests can further assist identification.
Field identification & locations
Commonly found in river gravels, beaches, and glacial tills worldwide. A fresh broken surface, magnetism, visible grains, and hardness testing would improve identification.
