sedimentary

Chert (Flint)

Silicon Dioxide (SiO2)

Hardness: 7; Color: White, cream, tan, grey; Luster: Waxy to dull; Crystal structure: Microcrystalline (Cryptocrystalline); Cleavage: None (Conchoidal fracture); Specific gravity: 2.65

Hardness: 7
Color: White, cream, tan, grey
Luster: Waxy to dull

Identified June 21, 2026More sedimentary →

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Physical properties

Hardness: 7; Color: White, cream, tan, grey; Luster: Waxy to dull; Crystal structure: Microcrystalline (Cryptocrystalline); Cleavage: None (Conchoidal fracture); Specific gravity: 2.65

Formation & geological history

Formed as nodules or layered deposits in sedimentary rocks like limestone or chalk. It originates from the accumulation of siliceous remains of marine organisms (radiolarians/diatoms) that dissolve and reprecipitate as silica.

Uses & applications

Used historically for stone tools and weapons (arrowheads). Modern uses include road surfacing, jewelry (as jasper/agate), and as a component in certain ceramics.

Geological facts

Because it breaks with a conchoidal fracture, it creates sharp edges that were vital for early human survival in making cutting tools and spear tips.

Field identification & locations

Identify by its extreme hardness (scratches glass), waxy luster, and curved, shell-like (conchoidal) fracture surfaces. Commonly found in riverbeds or eroding out of limestone cliffs.