sedimentary

Sandstone (River Cobble)

Sandstone (principally composed of Quartz, SiO2)

Mohs hardness: 6-7 (quartz grains); Color: buff, light brownish-yellow, tan with darker iron oxide mineral veining; Luster: dull to earthy; Texture: granular, fine to medium-grained with river-worn smooth rounded edges and small solution pits.

Hardness: 6-7 (quartz grains)
Luster: dull to earthy

Identified July 23, 2026More sedimentary →

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Physical properties

Formation & geological history

Formed from the compaction and cementation of mineral particles or rock fragments (sand) over geological timescales, typically in riverbeds, lakes, or ocean environments. This specific piece has undergone river transport (fluvial erosion), producing its rounded cobble shape.

Uses & applications

Commonly used in construction, landscaping, flagstones, and paving. As a river rock, it is widely used decoratively in garden paths, aquariums, and rock gardens.

Geological facts

River pebbles and cobbles often display unique cross-cutting veins or iron oxide banding, which reveal the pressure and chemical fluid movement present prior to erosion from the bedrock source.

Field identification & locations

Identified by its gritty sand-like granular texture, tan color, and water-worn rounded contours. Found in abundance in gravel bars, river beds, beaches, and sedimentary rock formations worldwide.

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