sedimentary

Chert (Jasper/Flint variety)

Microcrystalline quartz (SiO2)

Hardness: 6.5-7 on Mohs scale. Color: Tan, brown, and yellowish-opaque. Luster: Dull to waxy. Crystal structure: Trigonal (microcrystalline/cryptocrystalline). Cleavage: None (conchoidal fracture). Specific gravity: 2.65.

Hardness: 6
Color: Tan, brown, and yellowish-opaque
Luster: Dull to waxy

Identified June 27, 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 through the chemical replacement of limestone/dolomite by silica-rich fluids. Generally found in marine sedimentary layers ranging from Precambrian to Cenozoic eras.

Uses & applications

Historically used for stone tools (arrowheads, scrapers) due to conchoidal fracturing. Modernly used as road aggregate, in jewelry as Jasper, and for fire-starting (flint).

Geological facts

Chert is so durable that it often remains as gravel in riverbeds long after the surrounding limestone host rock has weathered away. It was one of the first materials used by early humans for tool-making.

Field identification & locations

Identify in the field by its hardness (it will scratch glass), smooth waxy feel on broken surfaces, and lack of visible grains. It is extremely common in riverbeds and limestone outcrops globally.

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