sedimentary
Banded Sandstone (River Cobble)
Arenite Sandstone with heavy mineral layering
Hardness: 6-7 (Mohs scale), Color: tan, grey, and dark brown bands, Luster: dull to earthy, Structure: Clastic with distinct bedding planes, Texture: fine to medium grained.
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Physical properties
Hardness: 6-7 (Mohs scale), Color: tan, grey, and dark brown bands, Luster: dull to earthy, Structure: Clastic with distinct bedding planes, Texture: fine to medium grained.
Formation & geological history
Formed via the deposition of sand-sized mineral particles or rock fragments in layers. The banding represents changes in sediment supply or mineral concentration over time, later lithified and water-worn into a smooth cobble shape.
Uses & applications
Primarily used as decorative landscaping stones, aquarium decor, or as meditation stones due to their smooth texture. Fine-grained sandstone is used in construction and abrasive manufacturing.
Geological facts
The smooth, oval shape is the result of mechanical weathering, likely in a riverbed or coastal environment where water friction has rounded the sharp edges over centuries.
Field identification & locations
Identify by looking for distinct parallel layers (bedding) and a gritty sand-paper feel on unpolished surfaces. Common in riverbeds and glacial deposits. Collectors value them for their aesthetic striping.
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