Chert (Flint Nodules)

Physical Properties

Hardness: 7 on Mohs scale; Color: typically grey, black, or brown with a tan limestone cortex; Luster: waxy to dull; Crystal structure: cryptocrystalline; Cleavage: none, shows conchoidal fracture.

Formation & Geological History

Formed through the accumulation of silica-rich organic remains (like diatoms or sponges) within limestone or chalk beds. Commonly associated with the Cretaceous period.

Uses & Applications

Historically used for stone tools and weapons (arrowheads). Modernly used in construction aggregate and for fire-starting in flintlock mechanisms.

Geological Facts

Flint was one of the first materials traded by prehistoric humans over long distances due to its ability to be knapped into sharp edges.

Field Identification & Locations

Identify by its waxy luster, extreme hardness (scratches glass), and smooth, curved (conchoidal) fracture surfaces. Often found as irregular nodules inside softer sedimentary rocks.

Identified on: 4/28/2026

Mode: Standard