sedimentary

Chert / Flint

Silicon dioxide (SiO2)

Hardness of 7 on the Mohs scale, colors ranging from grey, brown, white to black, waxy to vitreous luster, cryptocrystalline or microcrystalline quartz structure, exhibits conchoidal fracture with no cleavage, specific gravity of 2.60 to 2.65.

Identified July 28, 2026More sedimentary →

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Physical properties

Formation & geological history

Formed through the chemical precipitation of silica-rich fluids or replacement of calcium carbonate in limestone or chalk beds, primarily during the Cretaceous period and other geological epochs.

Uses & applications

Historically used for stone tools, arrowheads, and fire-starting (flint), and modernly used in abrasives, road construction, and decorative landscaping.

Geological facts

Chert and flint are chemically identical; the term 'flint' is often used for dark varieties found in chalk, while 'chert' is used for those in limestone. It was one of the most critical materials for early human technological development.

Field identification & locations

Easily identified by its conchoidal fracture (smooth, curved breakage patterns similar to broken glass), extremely high hardness capable of scratching glass, and waxy luster. Common globally in limestone and chalk formations.