sedimentary

Chert (Flint)

Microcrystalline Quartz (SiO2)

Hardness: 6.5-7 Mohs; Color: Grey, tan, white, or black; Luster: Dull to waxy; Structure: Cryptocrystalline; Cleavage: None (conchoidal fracture); Specific Gravity: 2.65

Hardness: 6
Color: Grey, tan, white, or black
Luster: Dull to waxy

Identified July 3, 2026More sedimentary →

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Physical properties

Hardness: 6.5-7 Mohs; Color: Grey, tan, white, or black; Luster: Dull to waxy; Structure: Cryptocrystalline; Cleavage: None (conchoidal fracture); Specific Gravity: 2.65

Formation & geological history

Formed through the accumulation of silica-rich organic remains (like diatoms or radiolaria) or chemical precipitation from groundwater within limestone or chalk beds. Often Paleozoic or Mesozoic age.

Uses & applications

Historically used for stone tools and weapons. Modern uses include road surfacing, decorative landscaping, and as a component in ceramics or glass.

Geological facts

Chert was one of the most important minerals for early humans because its conchoidal fracture creates edges sharper than a steel scalpel. It is also used in flintlock firearms to create sparks.

Field identification & locations

Identify by its waxy texture, extreme hardness (scratches glass), and shell-like (conchoidal) fracture patterns. Frequently found as nodules or layers within limestone outcrops.