sedimentary

River Cobble (Sandstone)

Arenite / Quartz Sandstone

Hardness: 6-7 (Mohs scale); Color: Gray, tan, and brownish; Luster: Dull/Earthy; Texture: Fine to medium grained with a gritty feel; Crystal structure: Clastic (composed of cemented sand grains); Cleavage: None

Hardness: 6-7 (Mohs scale)
Color: Gray, tan, and brownish
Luster: Dull/Earthy

Identified July 20, 2026More sedimentary →

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Physical properties

Formation & geological history

Formed through the accumulation and cementation of sand-sized mineral particles or rock fragments. This specific rounded shape is the result of long-term fluvial erosion (river action), which smoothed the edges during transport over many years.

Uses & applications

Commonly used in landscaping, as aggregate in construction, or as decorative stones in gardens and aquariums. Hand-sized smooth stones are also popular for rock painting.

Geological facts

Sandstone makes up about 20% to 25% of all sedimentary rocks on Earth. The rounded edges, or 'well-rounded' texture, indicate that the stone traveled a long distance from its original source before being collected.

Field identification & locations

Identify in the field by its gritty, sandpaper-like texture and rounded, water-worn exterior. It is commonly found in riverbeds, glacial tills, and coastal areas throughout the world.

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Sandstone or Siltstone

Arenite (if sandstone)

Sedimentary

Sedimentary Sandstone

Arenite (Sedimentary Rock)

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Fossiliferous Concretion

Septarian Concretion containing Brachiopods/Crinoids

fossil

Shale

Shale (clastic sedimentary rock)

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Brown Sandstone (River Rock)

Arenite

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Shale

Argillaceous sedimentary rock

sedimentary