sedimentary

Banded chert or siliceous mudstone

Microcrystalline quartz (chalcedony), SiO₂; possibly ferruginous shale

AI-generated identification · may be incorrect

Brown, opaque, fine-grained and earthy to slightly waxy, with thin pale bands or fractures and no visible crystals. Hardness is likely 6.5–7 if chert, with conchoidal fracture; specific gravity about 2.6.

Identified August 8, 2026More sedimentary →

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Physical properties

Formation & geological history

Likely formed when silica-rich sediment or biogenic silica lithified and recrystallized into microcrystalline quartz, with iron oxides producing the brown color. Exact age and locality cannot be determined from the photograph.

Uses & applications

Chert is used historically for sharp tools, fire-starting, aggregate, and decorative specimens; ordinary pieces have little commercial value.

Geological facts

Chert commonly preserves fossils or microscopic textures and can resemble weathered shale, jasper, or iron-rich mudstone.

Field identification & locations

Look for a very hard surface that scratches glass and breaks with smooth, curved edges; a streak test is generally white to pale brown. Common in sedimentary formations worldwide, including limestone and chalk sequences.