Chert (Flint)

Physical Properties

Hardness: 7 (Mohs scale); Color: Gray, brown, or black (often mottled); Luster: Waxy to dull; Crystal structure: Trigonal (microcrystalline); Cleavage: None (exhibits conchoidal fracture); Specific Gravity: 2.65.

Formation & Geological History

Formed through the accumulation of silica-rich organic remains (like diatoms or radiolarians) or chemical precipitation from groundwater. Often found as nodules within limestone or chalk beds, typically dating from the Paleozoic or Mesozoic eras.

Uses & Applications

Historically used for stone tools (arrowheads, knives) and sparking fire. Currently used in road surfacing, decorative landscaping, and occasionally as a low-cost gemstone when polished.

Geological Facts

Flint was the primary 'high-tech' material of the Stone Age due to its ability to produce razor-sharp edges. It is famous for its use in flintlock firearms to ignite gunpowder.

Field Identification & Locations

Identify in the field by its waxy texture and distinctive shell-like (conchoidal) fractures. It is commonly found in gravel pits, riverbeds, or embedded in carbonate rocks. It is harder than steel and will easily scratch glass.

Identified on: 4/24/2026

Mode: Standard