Chert (specifically Flint or Jasper variant)

Physical Properties

Hardness: 7 on Mohs scale; Color: Grayish-brown to reddish-brown; Luster: Waxy to dull; Crystal structure: Cryptocrystalline; Cleavage: None (conchoidal fracture); Specific gravity: 2.65

Formation & Geological History

Formed via the accumulation of siliceous remains of organisms (like diatoms or radiolarians) or through chemical precipitation in marine or groundwater environments. Found in nodules within limestone or chalk beds.

Uses & Applications

Historically used for stone tools (arrowheads, scrapers) due to its sharp edges; used in flintlock firearms and starting fires. Today used as a gemstone (Jasper), in construction aggregate, and for landscaping.

Geological Facts

Chert was one of the first materials used by early humans to create technology. It breaks with a conchoidal fracture, creating edges that can be sharper than a surgical scalpel.

Field Identification & Locations

Identify in the field by its waxy texture and shell-like (conchoidal) breaking pattern. It will easily scratch glass and generate sparks when struck against steel. Commonly found in riverbeds or eroding out of limestone cliffs.

Identified on: 4/19/2026

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