Chert (Flint)

Physical Properties

Hardness: 7 (Mohs scale), Color: Gray to Tan, Luster: Waxy to Dull, Crystal Structure: Cryptocrystalline, Cleavage: None (conchoidal fracture), SG: 2.65

Formation & Geological History

Formed by the precipitation of silica from groundwater or the accumulation of siliceous skeletal remains of diatoms and radiolarians in marine environments. Often found in limestone or chalk beds.

Uses & Applications

Historically used for stone tools and weapons (arrowheads). Today used for road surfacing, fire-starting strikers, and as a decorative landscape stone.

Geological Facts

Flint is a variety of chert that produces sparks when struck against steel. It was the primary material for the Stone Age technology that allowed early humans to survive.

Field Identification & Locations

Identified by its extremely smooth, waxy surface and sharp, curved (conchoidal) edges when broken. Commonly found in stream beds or as nodules in limestone outcrops.

Identified on: 5/2/2026

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