igneous
Dark river pebble, likely basalt or fine-grained volcanic rock
Basalt (probable); mostly plagioclase and pyroxene, with possible magnetite
AI-generated identification · may be incorrectSmooth, rounded, dark gray-black, and dull to subtly waxy, with a thin pale mineral vein or fracture fill. Likely Mohs hardness 5–6, fine-grained, massive, and lacking visible cleavage; exact density and composition require testing.
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Physical properties
Smooth, rounded, dark gray-black, and dull to subtly waxy, with a thin pale mineral vein or fracture fill. Likely Mohs hardness 5–6, fine-grained, massive, and lacking visible cleavage; exact density and composition require testing.
Formation & geological history
Probably formed from rapidly cooled mafic lava, then rounded by river, beach, or glacial transport; basalt commonly ranges from Precambrian to modern in age. The light line may be calcite, quartz, or weathered alteration material filling a crack.
Uses & applications
Suitable as a decorative pebble, paperweight, landscaping stone, or teaching specimen; not typically used as a gemstone or high-value ornamental material.
Geological facts
Its very fine texture indicates rapid cooling, preventing large crystals from developing. A streak, magnet, acid, and hardness test can help distinguish basalt from slate, chert, or industrial slag.
Field identification & locations
Common worldwide in volcanic regions and gravel deposits; inspect for vesicles, crystalline texture, and natural weathering. A magnet attraction suggests magnetite-rich basalt, while fizzing in dilute acid suggests a calcite vein.
