sedimentary

Chert (Flint)

Microcrystalline Quartz (SiO2)

AI-generated identification · may be incorrect

Hardness: 7 on Mohs scale; Color: tan, grey, and brown; Luster: waxy to dull; Structure: microcrystalline; Cleavage: none (conchoidal fracture); Specific gravity: 2.65

Hardness: 7 on Mohs scale
Color: tan, grey, and brown
Luster: waxy to dull

Identified July 8, 2026More sedimentary →

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Physical properties

Hardness: 7 on Mohs scale; Color: tan, grey, and brown; Luster: waxy to dull; Structure: microcrystalline; Cleavage: none (conchoidal fracture); Specific gravity: 2.65

Formation & geological history

Formed by the accumulation of silica-rich organic remains (like diatoms or radiolarians) or chemical precipitation from groundwater within limestone or chalk beds. Often Cretaceous in age.

Uses & applications

Historically used for stone tools and starting fires; currently used in construction aggregate and as decorative landscaping stones.

Geological facts

Because it breaks with a conchoidal (shell-like) fracture, it creates razor-sharp edges which is why it was the primary material for arrowheads and knives for millennia.

Field identification & locations

Identify by its extreme hardness (scratches glass), waxy feel, and smooth curved surfaces where it has chipped. Common in riverbeds and limestone outcrops worldwide.