sedimentary

Chert (White Chert / Flint)

Microcrystalline or Cryptocrystalline Quartz (SiO2)

Hardness: 7 on Mohs scale; Color: typically white, grey, or off-white; Luster: waxy to dull; Crystal structure: Trigonal (microcrystalline); Cleavage: none (conchoidal fracture); Specific gravity: 2.65.

Hardness: 7 on Mohs scale
Color: typically white, grey, or off-white
Luster: waxy to dull

Identified March 2, 2026More sedimentary →

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Physical properties

Formation & geological history

Formed from the accumulation of silica-rich organic remains (like diatoms or radiolaria) or chemical precipitation in marine environments. Often found as nodules within limestone or chalk beds. Geological age varies from Precambrian to Cenozoic.

Uses & applications

Historically used for stone tools (arrowheads, scrapers) due to conchoidal fracture. Industrially used in construction aggregate, road surfacing, and as a component in ceramics and glass-making.

Geological facts

Because of its high hardness and brittle nature, it produces very sharp edges when broken. It was a primary material used by Stone Age humans for survival tools and fire-starting (when struck against steel or pyrite).

Field identification & locations

Identify in the field by its extreme hardness (cannot be scratched by a steel nail) and characteristic curved, shell-like (conchoidal) fractures where broken. Commonly found in riverbeds, glacial till, and coastal cliffs.

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