igneous
Dark, water-worn pebble (likely basalt)
Likely basalt; identification is provisional from the photograph
AI-generated identification · may be incorrectFine-grained, dark brown-black, rounded, and slightly glossy from wear or moisture, with small lighter specks. Basalt is typically Mohs 5–6, with a fine-grained structure and no visible cleavage; the pebble’s density and exact mineral makeup cannot be determined visually.
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Physical properties
Fine-grained, dark brown-black, rounded, and slightly glossy from wear or moisture, with small lighter specks. Basalt is typically Mohs 5–6, with a fine-grained structure and no visible cleavage; the pebble’s density and exact mineral makeup cannot be determined visually.
Formation & geological history
If basalt, it formed when iron- and magnesium-rich lava cooled rapidly at or near the surface, then was rounded by water or abrasion. Its geological age is unknown and depends on its source.
Uses & applications
A common pebble is mainly suitable for collecting, landscaping, or decorative use; basalt is also widely used as aggregate and paving stone.
Geological facts
Basalt commonly contains plagioclase feldspar and pyroxene, sometimes with olivine. The visible pale flecks could be mineral grains or surface deposits, so they are not diagnostic in this image.
Field identification & locations
Its rounded shape indicates transport or abrasion, but color alone cannot confirm basalt; check for a uniformly fine-grained interior and relatively high density. Basalt pebbles occur in streams, beaches, and areas with volcanic rocks.
