Chert (specifically Flint or Jasper variant)

Physical Properties

Hardness: 7 on Mohs scale; Color: Gray, brown, or tan with dark outer cortex; Luster: Waxy to dull; Crystal structure: Trigonal (microcrystalline); 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 through the chemical replacement of limestone/chalk by silica-rich fluids. Can be found in geological formations ranging from the Precambrian to the Cenozoic.

Uses & Applications

Historically used for stone tools and weapons due to sharp edges when fractured; modernly used as road aggregate, architectural stone, and for fire-starting (flint and steel).

Geological Facts

Chert was one of the most important minerals for early humans, providing the material for arrowheads and knives. It is essentially the same mineral as chalcedony but with different impurities and formation environments.

Field Identification & Locations

Identify by its characteristic 'conchoidal' fracture (curved, glass-like breaks) and that it cannot be scratched by a steel knife. Commonly found as nodules in limestone or chalk beds globally.

Identified on: 4/22/2026

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