Chert / Flint

Physical Properties

Hardness: 6.5-7 (Mohs), Color: light gray, tan to brown, Luster: waxy to dull, Cleavage: none, exhibits conchoidal fracture.

Formation & Geological History

Formed from silica-rich fluids precipitating in limestone or chalk, or from the accumulation of siliceous marine microfossils (like radiolarians).

Uses & Applications

Historically used for making stone tools (arrowheads, scrapers) due to its conchoidal fracture. Sometimes used as a sparkstriker with steel.

Geological Facts

Because of its ability to hold a sharp edge, chert was one of the most important minerals for early human survival.

Field Identification & Locations

Identify by its waxy luster, hardness (scratches glass), and prominent curved, conchoidal fractures. Commonly found as nodules in sedimentary rock formations.

Identified on: 4/26/2026

Mode: Advanced