Chert (Nodule)

Physical Properties

Hardness: 7 (Mohs scale), Color: Brown, grey, and tan banding, Luster: Dull to waxy, Crystal Structure: Cryptocrystalline, Cleavage: None (conchoidal fracture), Specific Gravity: 2.6-2.7

Formation & Geological History

Formed by the precipitation of silica in sedimentary environments, often replacing calcium carbonate in limestones. This occurs through diagenesis over millions of years.

Uses & Applications

Historically used for stone tools and weapons (flintknapping) due to its sharp edges. Currently used in road construction, as an abrasive, and decorative landscaping.

Geological Facts

Chert is extremely durable and chemically stable. Its conchoidal fracture pattern allows it to break into edges that are sharper than a surgical scalpel. It can range in age from the Precambrian to the present.

Field Identification & Locations

Identify in the field by its hardness (scratches glass), waxy luster on fresh surfaces, and distinctive shell-like (conchoidal) fractures. Often found in limestone beds or as weathered pebbles in stream beds.

Identified on: 4/21/2026

Mode: Standard