sedimentary
River Cobble (Quartz-rich Sandstone)
Arenite with iron oxide staining
Hardness: 6-7 Mohs; Color: Tan, grey, and rusty orange/brown; Luster: Dull/earthy; Texture: Fine to medium-grained; Shape: Rounded/sub-rounded due to water erosion.
- Hardness
- 6-7 Mohs
- Color
- Tan, grey, and rusty orange/brown
- Luster
- Dull/earthy
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Physical properties
Hardness: 6-7 Mohs; Color: Tan, grey, and rusty orange/brown; Luster: Dull/earthy; Texture: Fine to medium-grained; Shape: Rounded/sub-rounded due to water erosion.
Formation & geological history
Formed through the accumulation and cementation of mineral grains (mostly quartz) in a high-energy water environment like a riverbed or beach. The orange staining is due to the oxidation of iron-bearing minerals (limonite/hematite).
Uses & applications
Primarily used as landscaping stone, river rock for decorative gardens, or as a source of aggregate for construction and road building.
Geological facts
The rounded shape indicates that this rock has traveled a long distance in a river or stream, where constant tumbling smoothed its once-agular edges.
Field identification & locations
Identify by its gritty sandpaper feel and extreme hardness (quartz will scratch glass). Commonly found in stream beds, glacial tills, and alluvial deposits.
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