sedimentary

Banded chert (likely flint)

Microcrystalline quartz/chalcedony, SiO₂

AI-generated identification · may be incorrect

Hardness about 6.5–7 Mohs; gray to tan with a dark gray band, dull to waxy luster, very fine-grained and massive, with conchoidal fracture and no cleavage. The pale coating may be weathering or surface carbonate residue.

Identified August 11, 2026More sedimentary →

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Physical properties

Formation & geological history

Chert forms when silica from organisms or groundwater replaces sediment and lithifies, commonly in limestone or marine beds. Individual pieces may be Paleozoic–Cenozoic, but age cannot be determined from the photograph.

Uses & applications

Used historically for cutting tools and fire-starting, and today as aggregate, landscaping stone, and a modest lapidary material. Attractive banded pieces may be polished.

Geological facts

Its sharp conchoidal edges and glassy-looking fracture distinguish it from most ordinary gravel. Flint is generally the dark, dense variety of chert.

Field identification & locations

Look for dense, nonporous texture, waxy surfaces, curved fractures, and resistance to scratching glass; common in sedimentary regions and glacial or river gravels. A photograph cannot confirm the identification without hardness or streak tests.