sedimentary

Chert (Flint)

Microcrystalline Quartz (SiO2)

Hardness: 6.5-7 on Mohs scale; Color: typically grey, brown, or black; Luster: waxy to dull; Structure: microcrystalline/cryptocrystalline; Cleavage: none (conchoidal fracture); Specific Gravity: 2.5-2.8.

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

Identified May 29, 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 chemical precipitation from groundwater within sedimentary beds, often replacing limestone or chalk.

Uses & applications

Historically used for stone tools and weapons due to its sharp edges when fractured. Modern uses include road surfacing, decorative landscaping, and as a component in glass making.

Geological facts

Chert was one of the most important materials for early humans because of its predictable conchoidal fracture, allowing it to be chipped into extremely sharp blades, scrapers, and arrowheads.

Field identification & locations

Identify in the field by its very smooth, glass-like fracture surfaces and extreme hardness (it will easily scratch a steel knife blade). Commonly found as nodules in limestone or as layered beds.