Chert (variations include Flint or Jasper)

Physical Properties

Hardness: 7 on Mohs scale; Color: Gray, brown, or dull red; Luster: Waxy to dull; Crystal structure: Cryptocrystalline (microscopic); Cleavage: None (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 in marine or groundwater environments. Found globally in limestone and chalk deposits.

Uses & Applications

Historically used for stone tools (arrowheads, scrapers) due to its sharp edges; used today in road construction, and certain colorful varieties (Jasper) are used in jewelry.

Geological Facts

Chert was one of the most vital materials for early humans because its conchoidal fracture creates edges sharper than a steel scalpel. It is also famous for its ability to produce sparks when struck against steel.

Field Identification & Locations

Identify by its waxy texture, extreme hardness (it will scratch glass), and curve-like (conchoidal) fractures. Found frequently as nodules or layers within sedimentary rock outcrops.

Identified on: 5/11/2026

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