Chert (Flint)

Physical Properties

Hardness: 7 on Mohs scale; Color: Gray, tan, or white with waxy luster; Crystal Structure: Cryptocrystalline; Cleavage: None (conchoidal fracture); Specific Gravity: 2.65

Formation & Geological History

Formed through the accumulation of silica-rich organic remains (like radiolarians or diatoms) or chemical precipitation in marine environments. Often found as nodules in limestone or chalk beds.

Uses & Applications

Historically used for stone tools and starting fires (sparking). Modern uses include road surfacing, abrasives, and as a component in jewelry (jasper/agate varieties).

Geological Facts

Chert was one of the most important minerals for early humans because its conchoidal fracture produces extremely sharp edges, ideal for arrowheads and scrapers.

Field Identification & Locations

Identify by its waxy appearance, extreme hardness (scratches glass), and shell-like (conchoidal) breakage patterns. Found globally in sedimentary basins.

Identified on: 4/29/2026

Mode: Standard