sedimentary

Likely weathered chert or siliceous shale

Cryptocrystalline quartz (SiO₂), possibly with clay minerals

AI-generated identification · may be incorrect

Gray-brown, dull to slightly waxy luster, opaque, fine-grained and irregularly fractured; likely hardness 6.5–7 if chert, with no visible cleavage. The image alone cannot distinguish it confidently from dense shale or a weathered fine-grained metamorphic rock.

Identified August 26, 2026More sedimentary →

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Physical properties

Formation & geological history

Most likely formed from silica-rich sediment or biogenic silica that lithified and/or replaced carbonate sediment; age depends on its source formation. Surface weathering has produced the brown coating and softened edges.

Uses & applications

Chert is used historically for cutting tools and occasionally as aggregate; ordinary specimens have little commercial or jewelry value. If shale, it is mainly useful as a geological or teaching specimen.

Geological facts

A fresh chert fracture is typically sharply conchoidal and glass-like, while shale splits into thin layers. The specimen appears dense and fractured but lacks enough visible texture for a definitive identification.

Field identification & locations

Test an inconspicuous edge with a steel nail: chert resists scratching, whereas shale usually scratches more easily and shows planar layering. Common sources include limestone terrains and sedimentary basins worldwide.