sedimentary

Chert (Nodule)

Silicon Dioxide (SiO2)

Hardness: 7 (Mohs scale); Color: Tan, brown, grey, and cream; Luster: Dull to waxy; Crystal Structure: Microcrystalline/Cryptocrystalline; Cleavage: None (conchoidal fracture); Specific Gravity: 2.6 – 2.7.

Hardness: 7 (Mohs scale)
Color: Tan, brown, grey, and cream
Luster: Dull to waxy

Identified March 30, 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 via chemical precipitation in limestone or chalk beds. It typically develops in marine environments as nodules or layered beds over millions of years.

Uses & applications

Historically used for making stone tools (arrowheads, scrapers) due to its sharp edges when fractured. Modernly used in road construction, as an abrasive, and small polished pieces are used in jewelry (as flint or jasper).

Geological facts

Chert is so hard it can easily scratch glass and even steel. It was one of the most important minerals for prehistoric humans because it produces a predictable, razor-sharp edge when struck with a hammerstone.

Field identification & locations

Identify in the field by its high hardness, smooth waxy texture, and unique shell-like (conchoidal) curved fractures. Commonly found in limestone outcrops, riverbeds, and as rounded nodules in chalk cliffs. Found globally.