sedimentary

Chert (Jasper/Flint variety)

Silicon Dioxide (SiO2)

Hardness: 7 (Mohs scale); Color: Dark brown to olive-greenish with mottling; Luster: Waxy to dull; Crystal structure: Microcrystalline/Cryptocrystalline (Trigonal); Cleavage: None (has conchoidal fracture); Specific gravity: 2.6 – 2.7.

Hardness: 7 (Mohs scale)
Color: Dark brown to olive-greenish with mottling
Luster: Waxy to dull

Identified April 12, 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 by chemical precipitation from hydrothermal fluids in marine or groundwater environments. This process often replaces pre-existing sedimentary rocks like limestone.

Uses & applications

Historically used for stone tools and starting fires (flint). Currently used in jewelry (as jasper), as an abrasive, and by collectors. Also used as road surfacing in some regions.

Geological facts

Chert is so hard it can scratch steel. It was one of the most vital materials for prehistoric humans because it fractures like glass into sharp, durable edges suitable for arrowheads and scrapers.

Field identification & locations

Identify in the field by its hardness and its 'conchoidal' (shell-like) fracture pattern. It often feels smooth and slightly greasy/waxy compared to surrounding limestone. Commonly found in riverbeds and limestone outcrops.

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