sedimentary

Chert (Jasper variety)

Silicon Dioxide (SiO2)

Hardness: 6.5-7 on Mohs scale; Color: Red-brown, tan, and earthy tones due to iron impurities; Luster: Dull to waxy; Structure: Microcrystalline quartz; Cleavage: None (conchoidal fracture); Specific Gravity: 2.6-2.65

Hardness: 6
Color: Red-brown, tan, and earthy tones due to iron impurities
Luster: Dull to waxy

Identified July 15, 2026More sedimentary →

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Physical properties

Formation & geological history

Formed through the accumulation of silica-rich microfossils or chemical precipitation from hydrothermal fluids in sedimentary environments. Common in marine limestone formations.

Uses & applications

Historically used for making stone tools and arrowheads; modernly used as decorative gravel, in lapidary work for jewelry, and as a polishing abrasive.

Geological facts

Chert has a conchoidal fracture which means it breaks like glass, producing sharp edges that were essential for prehistoric survival. Jasper is the name specifically given to opaque varieties of chert.

Field identification & locations

Identify by its hardness (it will scratch glass) and its smooth, shell-like fracture surfaces. Frequently found in riverbeds, glacial till, and within limestone outcrops.