sedimentary

Weathered chert or flint

Microcrystalline quartz (SiO₂), likely chert; exact variety uncertain from photo

AI-generated identification · may be incorrect

Tan-brown, opaque, dull to waxy luster with irregular conchoidal-looking fractures and a fine-grained texture. Mohs hardness about 7; no visible cleavage; specific gravity roughly 2.6. The lighter patches may be weathering or included silica/carbonate material.

Identified August 13, 2026More sedimentary →

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Physical properties

Formation & geological history

Chert forms when silica-rich groundwater or biological silica replaces sediment, commonly in limestone or other sedimentary beds. It may be Paleozoic or younger in the Duluth–northeastern Minnesota region, where glacial transport is also possible.

Uses & applications

Used historically for sharp tools and arrowheads; today it is mainly a teaching or collecting specimen and occasional aggregate material.

Geological facts

Fresh chert breaks with sharp, curved edges and can be confused with quartzite, jasper, or silicified limestone. The specimen’s small size and rounded weathering suggest a glacially transported pebble.

Field identification & locations

Commonly found in gravel, till, river deposits, and sedimentary outcrops around the Great Lakes. A steel file should barely scratch it; it should scratch ordinary glass, though testing may damage the specimen. A close inspection for fossils or carbonate reaction would refine the identification.