sedimentary

Chert (Flint)

Microcrystalline quartz (SiO2)

Hardness of 7 on the Mohs scale, typically brown, gray, or black, waxy to dull luster, cryptocrystalline structure, exhibits conchoidal fracture with very sharp edges, specific gravity around 2.60 to 2.65.

Identified August 3, 2026More sedimentary →

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Physical properties

Formation & geological history

Formed through the chemical precipitation of silica from aqueous solutions, often replacing carbonate rocks like limestone or accumulating from the skeletal remains of silica-secreting organisms such as radiolarians and diatoms during the Mesozoic and Paleozoic eras.

Uses & applications

Historically used extensively by ancient humans for making stone tools, arrowheads, and blades due to its conchoidal fracture. Today used in abrasive materials and historically for fire-starting.

Geological facts

Chert and flint are essentially the same material, though 'flint' is often reserved for darker varieties found in chalk formations. It was one of the most critical materials for early human technological development.

Field identification & locations

Easily identified by its characteristic waxy luster, conchoidal fracture, and extreme hardness that can easily scratch glass. Found globally in sedimentary sequences, particularly within limestone and chalk deposits.