Chert (Flint variety)

Physical Properties

Hardness: 6.5-7 (Mohs scale), Color: Dark brown to black, Luster: Waxy to vitreous, Crystal structure: Cryptocrystalline, Cleavage: None (conchoidal fracture)

Formation & Geological History

Formed by the accumulation of siliceous remains of organisms or chemical precipitation from silica-rich groundwater within sedimentary beds.

Uses & Applications

Used historically for stone tools and fire-starting; currently used in construction aggregates and occasionally as a laboratory abrasive.

Geological Facts

Because of its conchoidal fracture, it was the primary material for spearheads and arrowheads during the Stone Age. It produces sparks when struck against steel.

Field Identification & Locations

Look for a smooth, waxy texture and sharp, shell-like (conchoidal) edges where broken. Commonly found in limestone and chalk deposits.

Identified on: 5/7/2026

Mode: Standard