Chert / Flint

Physical Properties

Hardness: 6.5-7. Color: varying shades of red, brown, yellow, and gray due to impurities. Luster: waxy to dull. Cleavage: none, exhibits conchoidal fracture.

Formation & Geological History

Forms as chemical sedimentary rock, often as nodules in limestone or massive bedded deposits. The red/brown coloration typically comes from iron oxide impurities.

Uses & Applications

Historically used for making stone tools and starting fires. Currently used in road surfacing or simply collected.

Geological Facts

Because it breaks with a conchoidal fracture (producing sharp edges), it was one of the primary materials used by early humans for arrowheads and scrapers.

Field Identification & Locations

Identify by its hardness (scratches glass), waxy luster, and conchoidal fracture. Often found in riverbeds or limestone outcrops.

Identified on: 4/26/2026

Mode: Advanced