sedimentary

Chert (Flint)

Silicon dioxide (SiO2)

AI-generated identification · may be incorrect

Hardness: 7 (Mohs); Color: Grey, blue-grey, or black; Luster: Waxy to dull; Crystal structure: Microcrystalline (Cryptocrystalline); Cleavage: None (Conchoidal fracture); Specific gravity: 2.65

Hardness: 7 (Mohs)
Color: Grey, blue-grey, or black
Luster: Waxy to dull

Identified May 13, 2026More sedimentary →

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Physical properties

Hardness: 7 (Mohs); Color: Grey, blue-grey, or black; Luster: Waxy to dull; Crystal structure: Microcrystalline (Cryptocrystalline); Cleavage: None (Conchoidal fracture); Specific gravity: 2.65

Formation & geological history

Formed through the accumulation of siliceous remains of marine organisms (diatoms, radiolarians) or by chemical precipitation from silica-rich fluids in limestone or chalk beds.

Uses & applications

Historically used for stone tools and starting fires; currently used as a road aggregate, in jewelry (as jasper/agate varieties), and for flintlock mechanisms.

Geological facts

Chert was one of the most important minerals for early humans because its conchoidal fracture produces extremely sharp edges for knives and arrowheads.

Field identification & locations

Identify by its extreme hardness (scratches glass), waxy appearance on fresh surfaces, and characteristic 'shell-like' curved fracture patterns. Commonly found in nodules within limestone.