sedimentary

Chert (Flint)

Silicon Dioxide (SiO2)

Hardness: 6.5-7 Mohs; Color: Brown, gray, or reddish-brown; Luster: Waxy to vitreous; Crystal Structure: Microcrystalline (Cryptocrystalline); Cleavage: None (Conchoidal fracture); Specific Gravity: 2.6-2.7

Hardness: 6
Color: Brown, gray, or reddish-brown
Luster: Waxy to vitreous

Identified July 15, 2026More sedimentary →

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Physical properties

Formation & geological history

Formed as nodules or beds in sedimentary rocks like limestone or chalk when silica rich fluids precipitate out. Common in prehistoric to modern geological layers.

Uses & applications

Historically used for stone tools (arrowheads, scrapers) due to its sharp edges; used in modern times as a source of silica and in construction aggregates.

Geological facts

Flint is a variety of chert. When struck against steel, it creates sparks, which made it essential for early fire-starting and flintlock firearms.

Field identification & locations

Identify by its waxy luster, extreme hardness (scratches glass), and the way it breaks into sharp, curved (conchoidal) flakes. Often found in riverbeds or eroding out of limestone cliffs.