sedimentary

Chert (Jasper variety)

Silicon Dioxide (SiO2)

Hardness: 6.5-7 Mohs; Color: Brown, reddish-brown, tan, and white; Luster: Waxy to dull; Crystal structure: Microcrystalline/Cryptocrystalline; Cleavage: None (conchoidal fracture); Specific gravity: 2.65.

Hardness: 6
Color: Brown, reddish-brown, tan, and white
Luster: Waxy to dull

Identified June 30, 2026More sedimentary →

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Physical properties

Formation & geological history

Formed through the accumulation of silica-rich microfossils (like radiolaria or diatoms) or by chemical precipitation from silica-rich fluids within sedimentary rock layers. It is found in geological formations ranging from Precambrian to recent times.

Uses & applications

Historically used for making stone tools (arrowheads, scrapers) due to its sharp edges. Modernly used in landscaping, as a gemstone (jasper), and in some glass-making processes.

Geological facts

Chert is so hard that it was one of the primary materials used by prehistoric humans to spark fires and create weaponry. Jasper is a common variety of chert that contains iron oxide impurities, giving it its reddish or brownish hue.

Field identification & locations

Identify in the field by its conchoidal fracture (smooth, curved breaks like glass) and the fact that it cannot be scratched by a steel knife. It is commonly found in limestone or chalk beds and along riverbanks.