Igneous or Sedimentary
Pebble (Likely Basalt or Siltstone)
Clastic sedimentary rock or mafic volcanic rock
Hardness: 5-7 (Mohs scale), Color: Dark gray to charcoal, Luster: Dull/Matte, Texture: Fine-grained (Aphanitic), Shape: Sub-rounded due to water erosion.
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Physical properties
Hardness: 5-7 (Mohs scale), Color: Dark gray to charcoal, Luster: Dull/Matte, Texture: Fine-grained (Aphanitic), Shape: Sub-rounded due to water erosion.
Formation & geological history
Formed either from rapid cooling of magnesium-rich/iron-rich lava (if basalt) or accumulation of fine mineral particles in water (if siltstone). The rounded shape indicates it was transported by water or glaciers over a long period.
Uses & applications
Commonly used in landscaping, as aquarium decor, or as aggregate in construction and road paving.
Geological facts
River rocks and pebbles like this one are the result of thousands of years of mechanical weathering by moving water, which smooths out the jagged edges of the original parent rock.
Field identification & locations
Identify in the field by its smooth surface, lack of visible crystals to the naked eye, and uniform dark color. It is found globally in riverbeds, beaches, and glacial deposits.
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