Flint / Chert

Physical Properties

Hardness: 7 (Mohs), Color: Grey, black, or tan, Luster: Waxy to vitreous, Structure: Cryptocrystalline, Cleavage: None (conchoidal fracture), Specific Gravity: 2.65

Formation & Geological History

Formed in sedimentary rocks, typically as nodules in limestone or chalk through the replacement of calcium carbonate by silica. Often Cretaceous or Jurassic in age.

Uses & Applications

Historically used for tools (knapping), fire-starting (sparking with steel), and construction in flint-walled buildings. Used in high-grade ceramics and chemical industry.

Geological Facts

Flint is technically a variety of chert. It was the most important material for early human technology, used to make arrowheads and skinscrapers.

Field Identification & Locations

Identify by its characteristic conchoidal fracture (curved, shell-like breaks) and sharp edges. Common in coastal areas with chalk cliffs or river beds.

Identified on: 4/25/2026

Mode: Standard