Chert (Flint)

Physical Properties

Hardness: 7 (Mohs scale), Color: tan, grey, brown with darker inclusions, Luster: dull to waxy/greasy, Crystal Structure: Microcrystalline/Cryptocrystalline (rhombohedral), Cleavage: None (conchoidal fracture), Specific Gravity: 2.65

Formation & Geological History

Formed through the accumulation of silica-rich microfossils or precipitation from silica-rich fluids in sedimentary basins. It can occur in limestone as nodules or as thick bedded deposits.

Uses & Applications

Historical use for arrowheads and stone tools; modern use in abrasives, construction aggregate, and as a flint-starter for fires.

Geological Facts

Chert fracturs in a predictable conchoidal pattern, resulting in razor-sharp edges. This property made it the most vital material for early human technology (Stone Age tools).

Field Identification & Locations

Identify in the field by its hardness (scratches glass), waxy texture when fresh, and distinctive shell-like (conchoidal) fracture pattern when broken. Very common in riverbeds and limestone outcrops.

Identified on: 4/14/2026

Mode: Standard