igneous
Dark river pebble, likely basalt
Fine-grained basalt (probable; identification from image is uncertain)
AI-generated identification · may be incorrectDark gray to black, rounded and smooth from abrasion, with a dull to slightly lustrous surface; basalt is typically Mohs 5–6, fine-grained, and composed mainly of plagioclase and pyroxene, often with olivine. Crystal structure is too fine to distinguish individual grains in the image.
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Physical properties
Dark gray to black, rounded and smooth from abrasion, with a dull to slightly lustrous surface; basalt is typically Mohs 5–6, fine-grained, and composed mainly of plagioclase and pyroxene, often with olivine. Crystal structure is too fine to distinguish individual grains in the image.
Formation & geological history
Basalt forms when mafic lava cools at or near Earth’s surface; its age cannot be determined visually. The pebble’s rounded shape suggests transport and abrasion by water or sediment.
Uses & applications
Basalt is widely used as crushed aggregate, paving stone, and construction material; this small pebble is mainly decorative or collectible.
Geological facts
Basalt is among Earth’s most abundant volcanic rocks and also forms much of the ocean floor.
Field identification & locations
Look for a dense, dark, fine-grained texture and possible tiny crystals; a water-worn pebble can have a smooth oval shape. Basalt occurs worldwide, especially in volcanic regions and river deposits.
