sedimentary

Chert (Flint)

Chert (Silicon Dioxide, SiO2)

Hardness: 7 on Mohs scale; Color: Gray, brown, yellow, black; Luster: Waxy to dull; Crystal structure: Cryptocrystalline (microscopic quartz crystals); Cleavage: None (conchoidal fracture); Specific gravity: 2.65.

Hardness: 7 on Mohs scale
Color: Gray, brown, yellow, black
Luster: Waxy to dull

Identified April 3, 2026More sedimentary →

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Physical properties

Formation & geological history

Formed through the accumulation of silica-rich organic remains (like diatoms or radiolarians) or the chemical precipitation of silica in marine environments. Often found as nodules in limestone or chalk beds. This specimen appears water-worn.

Uses & applications

Historically used for making stone tools (arrowheads/knives) due to its sharp edges; used as a sparking agent in flintlock firearms; used today in road construction, as a landscaping stone, and occasionally in jewelry as polished stones.

Geological facts

Flint is a variety of chert that was the primary 'high-tech' material for prehistoric humans. When struck against steel or pyrite, it produces sparks that can start fires.

Field identification & locations

Identify by its extreme hardness (cannot be scratched by a steel knife) and its distinct shell-like (conchoidal) fracture pattern when broken. It is commonly found in riverbeds, glacial deposits, and chalk cliffs.