igneous
Dark water-worn pebble, probably basalt
Basalt (fine-grained mafic volcanic rock; identification is uncertain from the image alone)
AI-generated identification · may be incorrectSmooth, rounded, dark gray to black, with a dull to faintly waxy luster and no visible crystals. Basalt typically has Mohs hardness 5–6, interlocking microscopic plagioclase and pyroxene, and specific gravity around 2.8–3.0.
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Physical properties
Smooth, rounded, dark gray to black, with a dull to faintly waxy luster and no visible crystals. Basalt typically has Mohs hardness 5–6, interlocking microscopic plagioclase and pyroxene, and specific gravity around 2.8–3.0.
Formation & geological history
Basalt forms when iron- and magnesium-rich lava cools rapidly at or near Earth’s surface. It occurs in volcanic terrains of many ages; the pebble’s age and source cannot be determined visually.
Uses & applications
Basalt is widely used as crushed aggregate, paving stone, and building stone; this small pebble is mainly suitable for collecting or decoration.
Geological facts
The rounded shape and smooth surface suggest abrasion during transport in water or surf. The pale mark may be a surface inclusion or residue, not enough to identify a mineral.
Field identification & locations
A dark, fine-grained pebble without visible grains is consistent with basalt, but several other rocks can look similar; fresh-surface texture and hardness testing would help. Basalt pebbles are common near volcanic coasts and riverbeds.
