sedimentary

Chert (Jasper variety)

Silicon Dioxide (SiO2)

Hardness: 6.5-7 Mohs; Color: Reddish-brown, tan; Luster: Waxy to dull; Crystal structure: Microcrystalline/Cryptocrystalline; Cleavage: None (Conchoidal fracture); Specific gravity: 2.6-2.7

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

Identified June 25, 2026More sedimentary →

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Physical properties

Hardness: 6.5-7 Mohs; Color: Reddish-brown, tan; Luster: Waxy to dull; Crystal structure: Microcrystalline/Cryptocrystalline; Cleavage: None (Conchoidal fracture); Specific gravity: 2.6-2.7

Formation & geological history

Formed from the recrystallization of silica-rich microfossils (like radiolarians) or chemical precipitation in oceanic/sedimentary environments. It can occur as nodules or bedded layers in limestone or shale.

Uses & applications

Historically used for making stone tools; currently used in jewelry (as Jasper), aquarium gravel, and road construction material.

Geological facts

Chert is so hard it can produce sparks when struck against steel. The reddish variety is commonly called Jasper and has been used as a gemstone for thousands of years.

Field identification & locations

Identify by its waxy luster, extreme hardness (scratches glass), and smooth, shell-like (conchoidal) fractures. Found worldwide in stream beds and sedimentary rock outcrops.