Chert (Flint variety)

Physical Properties

Hardness: 7 (Mohs scale), Color: dull gray to dark brown with white rind, Luster: waxy to dull, Crystal structure: microcrystalline/cryptocrystalline, Cleavage: none (conchoidal fracture), Specific Gravity: 2.65

Formation & Geological History

Formed from the accumulation of silica-rich organic remains (like diatoms or radiolarians) or chemical precipitation in marine environments; typically found as nodules in limestone or chalk beds.

Uses & Applications

Historically used for stone tools and weapons (arrowheads); currently used in road construction, as decorative landscaping gravel, and as a sparking agent in fire-striking flint.

Geological Facts

Chert has an extremely sharp edge when broken due to its conchoidal fracture pattern. It was one of the most important minerals for early humans for tool development.

Field Identification & Locations

Identify in the field by its hardness (it will scratch glass), its shell-like (conchoidal) curved breaks, and it often has a lighter colored 'rind' on the exterior. Common in riverbeds and limestone outcrops.

Identified on: 4/13/2026

Mode: Standard