sedimentary

Chert (Flint)

Silicon dioxide (SiO2)

Hardness: 6.5-7 on Mohs scale; Color: typically brown, gray, or black; Luster: waxy to dull; Crystal structure: cryptocrystalline; Cleavage: none (conchoidal fracture); Specific gravity: 2.5-2.8.

Hardness: 6
Color: typically brown, gray, or black
Luster: waxy to dull

Identified June 7, 2026More sedimentary →

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Physical properties

Hardness: 6.5-7 on Mohs scale; Color: typically brown, gray, or black; Luster: waxy to dull; Crystal structure: cryptocrystalline; Cleavage: none (conchoidal fracture); Specific gravity: 2.5-2.8.

Formation & geological history

Formed through the accumulation of silica-rich organic remains (like diatoms or radiolarians) or chemical precipitation from hydrothermal fluids in sedimentary environments. Can be found in rock layers of various geological ages from Precambrian to Cenozoic.

Uses & applications

Used historically for making stone tools (arrowheads, scrapers) due to its sharp edges; used today as a decorative stone, in construction aggregate, and as 'flint' for fire-starting.

Geological facts

Chert was one of the most important minerals for early humans. Its unique ability to break into extremely sharp, predictable edges made it the primary material for the Stone Age tool industry.

Field identification & locations

Identify by its smooth, waxy surface and its characteristic conchoidal (shell-like) fracture pattern. Found globally, often as nodules in limestone or chalk beds.