sedimentary

Chert (Flint)

Microcrystalline Quartz (SiO2)

Hardness: 6.5-7 Mohs; Color: Grey, black, or brown with tan weathered rind; Luster: Waxy to dull; Structure: Cryptocrystalline; Cleavage: None (conchoidal fracture); Specific Gravity: 2.65

Hardness: 6
Color: Grey, black, or brown with tan weathered rind
Luster: Waxy to dull

Identified March 25, 2026More sedimentary →

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Physical properties

Hardness: 6.5-7 Mohs; Color: Grey, black, or brown with tan weathered rind; Luster: Waxy to dull; Structure: Cryptocrystalline; Cleavage: None (conchoidal fracture); Specific Gravity: 2.65

Formation & geological history

Forms primarily through the accumulation of silica-rich organic remains (like radiolarians or diatoms) or chemical precipitation from groundwater within limestone or chalk beds. Often dated from the Paleozoic and Mesozoic eras.

Uses & applications

Historically used for stone tools and weapons (arrowheads); currently used as a road aggregate, in glass manufacturing, and as a sparking agent in survival gear.

Geological facts

Flint was arguably the first 'industrial' mineral for humans, used for hundreds of thousands of years to create sharp-edged tools and to start fires through percussion.

Field identification & locations

Identify by its smooth, shell-like (conchoidal) fracture surfaces and its ability to scratch glass. Commonly found as nodules in limestone outcrops or as river-worn pebbles in gravel pits.