sedimentary

Chert (Flint)

Chert (̑SiO2)

Hardness: 7 (Mohs), Color: Gray, blue-gray, or tan, Luster: Waxy to vitreous, Structure: Microcrystalline/Cryptocrystalline, Cleavage: None (conchoidal fracture), Specific Gravity: 2.6-2.7

Identified June 8, 2026More sedimentary →

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Physical properties

Hardness: 7 (Mohs), Color: Gray, blue-gray, or tan, Luster: Waxy to vitreous, Structure: Microcrystalline/Cryptocrystalline, Cleavage: None (conchoidal fracture), Specific Gravity: 2.6-2.7

Formation & geological history

Formed via the accumulation of silica-rich organic remains (like radiolarians or diatoms) or by chemical precipitation from silica-rich fluids within sedimentary rock layers like limestone or chalk.

Uses & applications

Historically used for stone tools and weapons. Modernly used in construction aggregate, road surfacing, jewelry (as jasper or agate varieties), and as a fire-starter in survival gear.

Geological facts

Flint is a variety of chert that was essential to prehistoric humans for creating sharp-edged tools. When struck against steel, it produces sparks, which led to its use in flintlock firearms.

Field identification & locations

Identify by its characteristic waxy appearance and shell-like (conchoidal) fracture pattern when broken. It is commonly found in nodular or layered form within limestone outcrops and on riverbanks.