igneous
Rounded dark river pebble
Likely basaltic rock; exact identification requires testing
AI-generated identification · may be incorrectDark brown-black, fine-grained, and weakly lustrous with a smooth water-worn surface. Likely Mohs hardness 5–6, massive texture, no visible cleavage, and moderate-to-high specific gravity (~2.8–3.1).
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Physical properties
Dark brown-black, fine-grained, and weakly lustrous with a smooth water-worn surface. Likely Mohs hardness 5–6, massive texture, no visible cleavage, and moderate-to-high specific gravity (~2.8–3.1).
Formation & geological history
Probably formed as volcanic basalt or a related mafic igneous rock, then weathered and rounded by stream or beach transport. Basalt commonly formed during Cenozoic or older volcanic episodes; its age cannot be determined visually.
Uses & applications
Commonly used as landscaping stone, aggregate, decorative pebble, and occasionally in lapidary work. This individual is unlikely to have significant commercial or jewelry value.
Geological facts
The rusty brown surface likely reflects iron-oxide weathering, while the dark interior suggests mafic minerals such as pyroxene and plagioclase. A fresh broken surface would provide a more reliable identification.
Field identification & locations
Look for a dense, dark, fine-grained interior, lack of layering, and possible weak attraction to a magnet if magnetite is present; it should not fizz with dilute acid. Common in volcanic regions and alluvial river or beach gravels.
