sedimentary

Chert (Jasper)

Silicon Dioxide (SiO2)

Hardness: 6.5-7 on Mohs scale; Color: Reddish-brown, tan, or earth tones; Luster: Waxy to dull; Crystal structure: Microcrystalline/Cryptocrystalline (trigonal); Cleavage: None (conchoidal fracture); Specific gravity: 2.6-2.7

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

Identified July 19, 2026More sedimentary →

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Physical properties

Formation & geological history

Formed from the accumulation of silica-rich organic remains or chemical precipitation within sedimentary rock environments. Often found as nodules or beds in limestone or dolostone. Geological age ranges widely throughout the Phanerozoic eon.

Uses & applications

Historically used for stone tools/arrowheads due to its sharp conchoidal fracture. Currently used in landscaping, as aquarium gravel, and occasionally tumbled for jewelry or pocket stones.

Geological facts

Because it is composed of microcrystalline quartz, it is very resistant to physical and chemical weathering, meaning it often remains intact long after its host rock has eroded away. Jasper is the name specifically given to colorful, opaque varieties of chert.

Field identification & locations

Identify in the field by its hardness (it will scratch glass), waxy appearance, and smooth, curved (conchoidal) breaks. Typically found in riverbeds, glacial till, or eroding out of sedimentary outcrops.