sedimentary
River Cobble
Clastic Sedimentary (Quartz-rich Cobble)
Hardness: 6-7 Mohs; Color: Tan, grey, yellowish; Luster: Dull/Earthy; Crystal structure: Microcrystalline to massive; Cleavage: None; Specific gravity: Approx 2.65
- Hardness
- 6-7 Mohs
- Color
- Tan, grey, yellowish
- Luster
- Dull/Earthy
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Physical properties
Hardness: 6-7 Mohs; Color: Tan, grey, yellowish; Luster: Dull/Earthy; Crystal structure: Microcrystalline to massive; Cleavage: None; Specific gravity: Approx 2.65
Formation & geological history
Formed through the weathering and erosion of pre-existing bedrock, transported by water over long distances which smoothed and rounded the edges into a pebble/cobble shape through saltation.
Uses & applications
Commonly used in landscaping, construction aggregates, road base, and occasionally as decorative garden stones.
Geological facts
Rocks found in riverbeds act as natural grinders that erode the landscape and even themselves. The roundness indicates a relatively long history of exposure to high-energy water environments.
Field identification & locations
Identify in the field by its smooth, rounded, water-worn exterior and lack of sharp edges. Very common in riverbeds, glacial deposits, and coastal areas.
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