sedimentary

Chert (Jasper variety)

Silicon dioxide (SiO2)

Hardness: 6.5-7 on Mohs scale; Color: mottled brown, tan, and dark gray; Luster: vitreous to waxy; Structure: microcrystalline quartz; Fracture: conchoidal; Specific Gravity: 2.6-2.65

Hardness: 6
Color: mottled brown, tan, and dark gray
Luster: vitreous to waxy

Identified July 18, 2026More sedimentary →

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Physical properties

Hardness: 6.5-7 on Mohs scale; Color: mottled brown, tan, and dark gray; Luster: vitreous to waxy; Structure: microcrystalline quartz; Fracture: conchoidal; Specific Gravity: 2.6-2.65

Formation & geological history

Formed through the accumulation of silica-rich organic remains or chemical precipitation in sedimentary environments. Common in marine settings or replacing limestone/chalk beds.

Uses & applications

Used historically for stone tools and arrowheads due to conchoidal fracture. Modern uses include decorative landscaping, polished stones for jewelry (as jasper), and road construction aggregate.

Geological facts

Chert was one of the most important minerals for early humans because its predictable fracture pattern allowed it to be knapped into sharp edges. Large deposits are found in the Midwestern and Western United States.

Field identification & locations

Look for a smooth, waxy texture on fresh surfaces and a curved, glass-like (conchoidal) fracture. It is very hard and will easily scratch glass or a steel knife blade. It is commonly found in stream beds or eroded out of limestone cliffs.