Chert (Field Flint)

Physical Properties

Hardness: 6.5-7 on Mohs scale; Color: Tan, beige, or white with a weathered yellowish rind (cortex); Luster: Waxy to dull; Structure: Cryptocrystalline; Cleavage: None (conchoidal fracture); Specific Gravity: 2.65

Formation & Geological History

Formed through the accumulation of silica-rich organic remains or chemical precipitation in marine environments, often replacing limestone or chalk. Frequently found as nodules or beds in sedimentary layers.

Uses & Applications

Historically used for stone tools and starting fires; currently used as road aggregate, architectural filler, and by flintknappers for decorative arrowhead replicas.

Geological Facts

Chert is so hard it can scratch steel. It was one of the most vital materials for prehistoric humans because it breaks with incredibly sharp edges through conchoidal fracturing.

Field Identification & Locations

Identify in the field by its distinct waxy interior compared to a rough, chalky outer crust. It is commonly found in areas with limestone or chalk deposits globally. Use a scratch test; it will easily scratch glass.

Identified on: 5/13/2026

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