Chert (Flint)

Physical Properties

Hardness: 7 on Mohs scale; Color: typically white, gray, or brown with reddish iron staining; Luster: waxy to dull; Crystal structure: cryptocrystalline; Cleavage: none (conchoidal fracture); Specific gravity: 2.65.

Formation & Geological History

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

Uses & Applications

Historically used for stone tools (arrowheads, scrapers) and ignition sources (flint and steel). Currently used as a gemstone (Jasper varieties), in road construction, and as a refractory material.

Geological Facts

Because of its conchoidal fracture pattern, it breaks into extremely sharp edges, making it the primary material for prehistoric weapons. Some cherts contain well-preserved microfossils of early life forms.

Field Identification & Locations

Identify in the field by its hardness (scratches glass), waxy feel, and smooth, curved fracture surfaces. Found worldwide, particularly in areas with sedimentary limestone deposits.

Identified on: 4/28/2026

Mode: Standard