sedimentary

Sandstone (River Cobble)

Clastic sedimentary rock (primarily SiO2)

Hardness: 6-7 on Mohs scale (due to quartz content); Color: Tan, beige, or light brown; Luster: Dull/earthy; Structure: Clastic, fine to medium-grained; Cleavage: None (fractures across grains); Specific Gravity: 2.2-2.8.

Hardness: 6-7 on Mohs scale (due to quartz content)
Color: Tan, beige, or light brown
Luster: Dull/earthy

Identified July 8, 2026More sedimentary →

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Physical properties

Formation & geological history

Formed through the accumulation and cementation of sand-sized mineral grains or rock fragments, typically in fluvial (river), marine, or desert environments. This specific specimen shows significant rounding, indicating transport by water in a river or stream bed.

Uses & applications

Used widely in construction (dimension stone), as an abrasive in glass manufacturing, and as a natural material for landscaping and pathways.

Geological facts

Sandstone accounts for roughly 20 to 25 percent of all sedimentary rocks on Earth. The grains are typically held together by mineral cements like silica, calcium carbonate, or iron oxide.

Field identification & locations

Identify in the field by its gritty, sandpaper-like feel and visible grains. Rounded cobbles like this are common in current or ancient riverbeds and glacial deposits. Collectors often value them for their smooth, tactile shape.

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Brown Sandstone (River Rock)

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