sedimentary

Chert (Jasper/Flint variety)

Microcrystalline or Cryptocrystalline Quartz (SiO2)

Hardness: 7 (Mohs scale); Color: Variegated brown, tan, and gray; Luster: Waxy to dull; Crystal structure: Trigonal (microscopic); Cleavage: None (conchoidal fracture); Specific gravity: 2.6 – 2.65.

Hardness: 7 (Mohs scale)
Color: Variegated brown, tan, and gray
Luster: Waxy to dull

Identified March 16, 2026More sedimentary →

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Physical properties

Formation & geological history

Formed through the accumulation of silica-rich organic remains (like diatoms or radiolarians) or via chemical precipitation in groundwater that replaces limestone or chalk. It is found in geological strata ranging from the Precambrian to the Cenozoic.

Uses & applications

Historically used for stone tools and weapons due to sharp edges; currently used for road surfacing, gravel, and occasionally as semi-precious gemstones in jewelry (as Jasper).

Geological facts

Chert was one of the most important materials for early humans; it produces sparks when struck against steel, which made it the primary material for 'flintlock' firearms and fire-starting kits.

Field identification & locations

Identify in the field by its extreme hardness (cannot be scratched by a steel knife) and its smooth, shell-like (conchoidal) fracture pattern. Found globally in nodules within limestone or as bedded deposits.

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