sedimentary

River-worn sandstone cobble

Quartz-rich sandstone (arenite), likely ferruginous sandstone

AI-generated identification · may be incorrect

Hardness about 6–7; tan-brown with muted green-gray areas, dull to earthy luster, and rounded water-worn surfaces. Composed mainly of quartz grains with feldspar and iron-bearing cement; granular texture is suggested but individual grains are difficult to resolve.

Identified September 11, 2026More sedimentary →

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Physical properties

Formation & geological history

Originally lithified from compacted and cemented sand, probably in a river, beach, or nearshore environment; later rounded by abrasion during transport. Its precise geological age cannot be determined from the photograph.

Uses & applications

Primarily a natural decorative or teaching specimen; sandstone is widely used as building stone, paving, and aggregate. This cobble has little jewelry value.

Geological facts

The elongated, smooth shape indicates prolonged abrasion rather than crystal growth. Brown coloration commonly reflects iron-oxide cement or staining, while green-gray tones may indicate clay minerals or chlorite.

Field identification & locations

Look for visible sand grains, gritty texture, and possible subtle bedding; a steel nail usually does not scratch quartz-rich sandstone, though cement variation affects results. Common in stream gravels and glacial deposits worldwide.