sedimentary

Chert (includes Flint & Jasper)

Chert (Siliceous sedimentary rock, chemical formula SiO2)

Hardness: 7 on Mohs scale; Color: Variable (tan, grey, white, brown); Luster: Waxy to dull; Crystal structure: Microcrystalline/Cryptocrystalline (cannot see crystals with naked eye); Fracture: Conchoidal (shell-like curves); Specific Gravity: 2.5-2.8.

Hardness: 7 on Mohs scale
Color: Variable (tan, grey, white, brown)
Luster: Waxy to dull

Identified April 26, 2026More sedimentary →

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Physical properties

Formation & geological history

Formed through the accumulation of silica-rich organic remains (like diatoms or radiolaria) or via chemical precipitation from silica-rich fluids within limestone or chalk beds. It can date from the Precambrian to the present.

Uses & applications

Used historically for stone tools (arrowheads, scrapers) due to its sharp edges when broken. Today used as road surfacing, in landscaping, and occasionally as an abrasive or in gemstone tumbling (Jasper varieties).

Geological facts

Because of its unique fracture pattern, chert was the primary material used by prehistoric humans to start fires (when struck against steel or pyrite) and create weaponry. It is essentially a high-density version of quartz.

Field identification & locations

Identify by its waxy texture,extreme hardness (it will scratch glass), and the way it breaks into sharp, curved edges. Commonly found as nodules or layers within limestone formations globally.

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Sandstone or Siltstone

Arenite (if sandstone)

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Chert Breccia

Brecciated Chert (Microcrystalline Silica)

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Sandstone Grain

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Shale or Slaty Mudstone

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Sandstone

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