sedimentary

Weathered iron-rich river cobble

Ferruginous chert or iron-stained siliceous mudstone (tentative identification)

AI-generated identification · may be incorrect

Hardness likely 6–7 Mohs; rounded, opaque brown-gold and gray surface with dull to slightly waxy luster, fine-grained texture, and no visible cleavage. The coloration suggests iron oxides such as goethite or hematite in a silica-rich matrix.

Identified August 13, 2026More sedimentary →

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Physical properties

Formation & geological history

Probably formed from silicified sediment or chert, later exposed to weathering and rounded by stream or beach transport; its precise geological age and locality cannot be determined from the photograph.

Uses & applications

Typically a collecting specimen or field curiosity; dense chert can be used for knapping and occasionally as aggregate, but this individual has little commercial value unless unusually attractive or proven to be a gemstone material.

Geological facts

Iron staining commonly produces orange, ochre, brown, and gray zoning in chert and other siliceous rocks. The smooth oval shape indicates substantial abrasion in moving water or surf.

Field identification & locations

Look for a glassy or waxy fracture, lack of fizz in dilute hydrochloric acid, and the ability to scratch ordinary glass; a steel file may leave little mark. Common sources include stream gravels and weathered sedimentary terrains worldwide.