sedimentary

Chert (Flint)

Silicon Dioxide (SiO2)

Hardness: 6.5-7 on Mohs scale; Color: Grey, black, or brown; Luster: Waxy to dull; Crystal Structure: Microcrystalline/Cryptocrystalline; Cleavage: None (conchoidal fracture); Specific Gravity: 2.65.

Hardness: 6
Color: Grey, black, or brown
Luster: Waxy to dull

Identified May 9, 2026More sedimentary →

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Physical properties

Hardness: 6.5-7 on Mohs scale; Color: Grey, black, or brown; Luster: Waxy to dull; Crystal Structure: Microcrystalline/Cryptocrystalline; Cleavage: None (conchoidal fracture); Specific Gravity: 2.65.

Formation & geological history

Formed by the accumulation of siliceous remains of marine organisms (like diatoms or radiolarians) or through the chemical precipitation of silica in groundwater within limestone or chalk beds. Often Cretaceous in age.

Uses & applications

Historically used for stone tools and weapons due to its sharp edges; used in modern times for road surfacing, as a component in ceramics, and by flintknappers for primitive technology demonstrations.

Geological facts

Flint was one of the first minerals ever 'mined' by humans. It is famous for its ability to create sparks when struck against steel, which was the primary method for igniting primitive firearms like flintlocks.

Field identification & locations

Identify by its characteristic conchoidal (shell-like) fracture pattern and smooth, waxy surface. It is often found as nodules inside chalk or limestone or as weathered pebbles in riverbeds and on beaches.