sedimentary
River Stone (likely Siltstone or Mudstone)
Argillaceous Sedimentary Rock
Dull to earthy luster (when dry), dark brown to charcoal color, fine-grained texture, hardness approximately 3-5 on Mohs scale, smooth water-worn surface, lacks visible crystals.
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Physical properties
Dull to earthy luster (when dry), dark brown to charcoal color, fine-grained texture, hardness approximately 3-5 on Mohs scale, smooth water-worn surface, lacks visible crystals.
Formation & geological history
Formed by the compaction of silt and clay particles in low-energy aquatic environments like floodplains or lake bottoms. This specific specimen has been rounded and polished through fluvial erosion in a river or stream.
Uses & applications
Commonly used for landscaping, decorative garden stones, aquarium hardscaping, and as aggregate in construction. High-quality smooth stones are often used in stone massage therapy.
Geological facts
River stones get their smooth, rounded shape through a process called saltation, where they are tumbled along the riverbed, knocking off sharp edges and polishing the surface over years of water movement.
Field identification & locations
Identify in the field by its rounded, smooth shape and lack of sharp edges. Typically found in active or ancient riverbeds. To confirm type, look for layering (bedding) or fine-grained texture when split.
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