sedimentary

Chert (Flint)

Microcrystalline Quartz (SiO2)

Hardness: 7 Mohs; Color: Grey, brown, tan, translucent smoky; Luster: Waxy to vitreous; Crystal Structure: Cryptocrystalline; Cleavage: None (conchoidal fracture); Specific Gravity: 2.65

Hardness: 7 Mohs
Color: Grey, brown, tan, translucent smoky
Luster: Waxy to vitreous

Identified July 13, 2026More sedimentary →

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Physical properties

Hardness: 7 Mohs; Color: Grey, brown, tan, translucent smoky; Luster: Waxy to vitreous; Crystal Structure: Cryptocrystalline; Cleavage: None (conchoidal fracture); Specific Gravity: 2.65

Formation & geological history

Formed by the precipitation of silica from groundwater or the accumulation of silica-rich organic remains (like radiolarians) in marine environments. Often found as nodules within limestone or chalk beds.

Uses & applications

Used historically for stone tools and weapons (arrowheads); currently used in road construction, as a source of silica for glass, and for decorative landscape stone.

Geological facts

Flint is a variety of chert that has a distinct conchoidal fracture, allowing it to be chipped into extremely sharp edges. It was one of the most vital materials for early human survival for both tools and fire-starting.

Field identification & locations

Identify by its waxy appearance, extreme hardness (scratches glass), and the way it breaks into curved, shell-like flakes. Common in sedimentary basins worldwide.