sedimentary

Chert (Flint)

Silicon Dioxide (SiO2)

Hardness: 7 on Mohs scale; Color: Tan, white, grey, with black rinds; Luster: Waxy to dull; Breakage: Conchoidal (shell-like) fracture; Structure: Microcrystalline or cryptocrystalline quartz.

Hardness: 7 on Mohs scale
Color: Tan, white, grey, with black rinds
Luster: Waxy to dull

Identified July 20, 2026More sedimentary →

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Physical properties

Hardness: 7 on Mohs scale; Color: Tan, white, grey, with black rinds; Luster: Waxy to dull; Breakage: Conchoidal (shell-like) fracture; Structure: Microcrystalline or cryptocrystalline quartz.

Formation & geological history

Formed in marine environments through the precipitation of silica-rich fluids or the accumulation of siliceous skeletal remains (like diatoms/radiolarians) within limestone or chalk beds.

Uses & applications

Historically used for stone tools (arrowheads, scrapers) and fire-starting; currently used in road construction, as an abrasive, and for decorative landscaping.

Geological facts

Chert is so hard it can scratch steel. Because of its predictable conchoidal fracture, it was the most important material for prehistoric tool-making for hundreds of thousands of years.

Field identification & locations

Look for a smooth, waxy surface on fresh breaks and a chalky outer 'cortex' or rind. It is often found as nodules inside limestone or as jagged fragments in stream beds. Common worldwide.