sedimentary

Chert (Flint)

Chert (Cryptocrystalline silicon dioxide, SiO2)

AI-generated identification · may be incorrect

Hardness: 7 on Mohs scale; Color: Gray, tan, or brown; Luster: Waxy to dull; Crystal structure: Cryptocrystalline; Cleavage: None (conchoidal fracture); Specific gravity: 2.65

Hardness: 7 on Mohs scale
Color: Gray, tan, or brown
Luster: Waxy to dull

Identified June 22, 2026More sedimentary →

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Physical properties

Hardness: 7 on Mohs scale; Color: Gray, tan, or brown; Luster: Waxy to dull; Crystal structure: Cryptocrystalline; Cleavage: None (conchoidal fracture); Specific gravity: 2.65

Formation & geological history

Formed from the accumulation of siliceous remains of microscopic organisms (diatoms, radiolarians) or through chemical precipitation in marine or freshwater environments. Often found as nodules in limestone or chalk beds.

Uses & applications

Historically used for stone tools and weapons due to its sharp edges; used in modern times for industrial grinding media and as flint for fire-starting. Occasionally used in jewelry as decorative stones.

Geological facts

Chert has been used by humans for hundreds of thousands of years to create arrowheads and scrapers. When struck against steel, it can produce sparks, which led to its extensive use in flintlock firearms.

Field identification & locations

Identify in the field by its very smooth ‘waxy’ texture and sharp, shell-like (conchoidal) fractures where broken. It is harder than steel and will scratch a glass plate. Common in riverbeds and limestone outcrops.