sedimentary
River Rock (River Cobbles)
Fluvial Conglomerate Clasts (primarily composed of various minerals such as Quartz, SiO2)
Hardness: 6-7 (Mohs scale), Color: shades of grey, tan, and brown, Luster: dull to earthy (waxy when wet), Crystal structure: varies by clast type (mostly microcrystalline), Cleavage: none, Specific Gravity: 2.6-2.7
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Physical properties
Hardness: 6-7 (Mohs scale), Color: shades of grey, tan, and brown, Luster: dull to earthy (waxy when wet), Crystal structure: varies by clast type (mostly microcrystalline), Cleavage: none, Specific Gravity: 2.6-2.7
Formation & geological history
Formed through fluvial processes where rocks are transported by river currents. Continuous tumbling in water smooths and rounds the edges over thousands of years. Usually found in Quaternary or Holocene alluvial deposits.
Uses & applications
Used extensively in construction for drainage, landscaping, decorative stone for gardens/walkways, and as aggregate for concrete and asphalt.
Geological facts
River rocks are often 'recycled' by nature; they can be eroded from ancient mountains, buried in sedimentary basins, and then unearthed again millions of years later by modern rivers.
Field identification & locations
Identify in the field by their smooth, rounded ('mature') shape and lack of sharp edges. Commonly found in riverbeds, floodplains, and glacial outwash plains. Look for imbrication (layering) in dry beds to determine past water flow direction.
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