sedimentary

Rounded quartz-rich river cobble

Likely quartzite or quartz-rich sandstone (SiO₂-dominant), possibly weathered chert

AI-generated identification · may be incorrect

Hardness approximately 6.5–7 Mohs; tan, cream, gray, and rusty-brown surface with dull to locally glassy luster. Rounded by abrasion, massive and non-cleaving; apparent granular texture suggests quartz grains cemented into a durable rock.

Identified September 15, 2026More sedimentary →

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Physical properties

Formation & geological history

Most likely formed from compacted and silica-cemented sand, then hardened and rounded during transport in a river or beach environment. Its precise geological age cannot be determined from the photograph.

Uses & applications

Commonly collected as a natural specimen or used decoratively in landscaping, aquaria, and craft work; not typically valuable as a gemstone.

Geological facts

The smooth shape records prolonged abrasion and transport, while reddish patches likely reflect iron-oxide staining. A conclusive identification requires a fresh surface, hardness testing, and ideally acid and microscopic examination.

Field identification & locations

Look for abundant quartz grains, resistance to scratching, and no reaction to dilute hydrochloric acid; quartzite generally scratches glass and steel, whereas softer sandstone may not. Quartz-rich cobbles occur widely in river gravels and glacial deposits.