sedimentary

Chert (Flint)

Microcrystalline or Cryptocrystalline Quartz (SiO2)

AI-generated identification · may be incorrect

Hardness: 7 on Mohs scale; Color: Gray, brown, or tan with waxy/greasy luster; Structure: Microcrystalline; Cleavage: None (conchoidal fracture); Specific Gravity: 2.65.

Hardness: 7 on Mohs scale
Color: Gray, brown, or tan with waxy/greasy luster

Identified March 25, 2026More sedimentary →

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Physical properties

Hardness: 7 on Mohs scale; Color: Gray, brown, or tan with waxy/greasy luster; Structure: Microcrystalline; Cleavage: None (conchoidal fracture); Specific Gravity: 2.65.

Formation & geological history

Formed through the accumulation of silica-rich organic remains (like diatoms or sponges) on the ocean floor or through chemical precipitation in limestone or dolomite beds. Often found as nodules or layers.

Uses & applications

Historically used for stone tools and weapons (arrowheads). Modern uses include road aggregate, decorative landscaping, and as a component in glass and ceramics.

Geological facts

Chert is a 'standard' for prehistoric toolmaking because of its predictable conchoidal fracture which creates razor-sharp edges. It can spark when struck against steel, leading to its name 'flint' in common parlance.

Field identification & locations

Identify by its hardness (will scratch glass), waxy feel, and sharp, curved (conchoidal) edges when broken. It is extremely common in areas with limestone bedrock across North America and Europe.