sedimentary

Chert (Flint)

Chert (Silicon Dioxide, SiO2)

AI-generated identification · may be incorrect

Hardness: 7 (Mohs scale); Color: Tan, beige, grey; Luster: Waxy to dull; Crystal structure: Cryptocrystalline (microscopic quartz); Cleavage: None (conchoidal fracture); Specific gravity: 2.65

Hardness: 7 (Mohs scale)
Color: Tan, beige, grey
Luster: Waxy to dull

Identified May 17, 2026More sedimentary →

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Physical properties

Hardness: 7 (Mohs scale); Color: Tan, beige, grey; Luster: Waxy to dull; Crystal structure: Cryptocrystalline (microscopic quartz); Cleavage: None (conchoidal fracture); Specific gravity: 2.65

Formation & geological history

Formed through the accumulation of silica-rich organic remains (like radiolarians or diatoms) or by chemical precipitation from groundwaters in limestone or chalk beds. Most common in ancient marine sedimentary sequences.

Uses & applications

Historically used for stone tools (arrowheads, scrapers) due to its sharp edges; modernly used in road construction, as a flux in glassmaking, and for fire-starting strikers.

Geological facts

Chert is so hard it will scratch glass and even common steel. It has been used by humans for hundreds of thousands of years to create sharp-edged tools and weapons.

Field identification & locations

Identify by its waxy appearance, extreme hardness, and conchoidal (shell-like) fracture patterns. It is frequently found as nodules within limestone or as bedded deposits in riverbeds and coastal cliffs.