sedimentary

Chert (Jasper variety)

Silicon Dioxide (SiO2)

Hardness: 6.5-7 on Mohs scale; Color: Reddish-brown, tan, or opaque earth tones; Luster: Waxy to dull; Crystal structure: Microcrystalline/Cryptocrystalline (trigonal); Cleavage: None (conchoidal fracture); Specific gravity: 2.58–2.91.

Hardness: 6
Color: Reddish-brown, tan, or opaque earth tones
Luster: Waxy to dull

Identified March 9, 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 hydrothermal fluids in sedimentary environments. Can be found in bedrock ranging from Precambrian to Cenozoic ages.

Uses & applications

Historically used for stone tools (knapping) due to sharp edges; currently used for lapidary work, jewelry (cabochons), and decorative landscaping stones.

Geological facts

Chert was one of the most important minerals for early humans to create arrowheads and scrapers. Jasper is a variety of chert that gets its red/brown color specifically from iron oxide inclusions.

Field identification & locations

Identify in the field by its very smooth, shell-like (conchoidal) fracture surfaces and its ability to scratch glass. Commonly found in riverbeds, glacial till, or as nodules in limestone/dolomite. Often feels heavier and denser than surrounding rocks.