sedimentary

Chert (Jasper variety)

Silicon Dioxide (SiO2)

Hardness: 6.5-7 Mohs; Color: Reddish-brown due to iron oxide inclusions; Luster: Dull to waxy; Structure: Microcrystalline; Cleavage: None (conchoidal fracture); Specific Gravity: 2.6-2.7

Hardness: 6
Color: Reddish-brown due to iron oxide inclusions
Luster: Dull to waxy

Identified June 25, 2026More sedimentary →

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Physical properties

Hardness: 6.5-7 Mohs; Color: Reddish-brown due to iron oxide inclusions; Luster: Dull to waxy; Structure: Microcrystalline; Cleavage: None (conchoidal fracture); Specific Gravity: 2.6-2.7

Formation & geological history

Formed through the accumulation of silica-rich microfossils or chemical precipitation of silica in sedimentary environments. Its reddish hue indicates oxidation during formation.

Uses & applications

Historically used for making stone tools (arrowheads). Modernly used in landscaping, as decor, and for lapidary work (tumbling and polishing).

Geological facts

Chert has been used by humans for millions of years because its conchoidal fracture creates edges sharper than a steel razor. Jasper is a variety of chert commonly found in many colors.

Field identification & locations

Identify by its waxy texture and sharp, curved fracture lines. It cannot be scratched by a steel knife. It is ubiquitous in sedimentary basins and riverbeds worldwide.