igneous
Tumbled dark river pebble, probably basalt
Fine-grained mafic volcanic rock, most likely basalt; exact identification requires testing
AI-generated identification · may be incorrectDark gray-black, smoothly water-worn or mechanically tumbled, with a dull to faintly satin luster and no obvious crystals. Basalt typically has hardness about 5–6 Mohs, negligible cleavage, fine interlocking crystals, and specific gravity around 2.8–3.1; the visible cavities may be vesicles or natural surface pits.
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Physical properties
Dark gray-black, smoothly water-worn or mechanically tumbled, with a dull to faintly satin luster and no obvious crystals. Basalt typically has hardness about 5–6 Mohs, negligible cleavage, fine interlocking crystals, and specific gravity around 2.8–3.1; the visible cavities may be vesicles or natural surface pits.
Formation & geological history
Likely formed as rapidly cooled lava, potentially millions to billions of years ago, then rounded by river or shoreline abrasion; alternatively it may be a shaped/tumbled landscaping or craft stone. Commonly sourced from volcanic terrains and stream gravels.
Uses & applications
Used as aggregate, riprap, landscaping stone, massage stones, and inexpensive craft or decorative material; not normally a jewelry gemstone.
Geological facts
The small holes could indicate vesicular basalt, but their placement and smoothness may also reflect intentional drilling or wear. A magnet response would support iron-rich basalt but is not diagnostic.
Field identification & locations
Look for a uniformly fine texture, dark color, substantial weight, and occasional tiny feldspar crystals; basalt generally leaves a weak-to-moderate streak and does not fizz with dilute hydrochloric acid. Common in volcanic regions worldwide.
