sedimentary

Chert (Jasper)

Silicon Dioxide (SiO2)

Hardness: 6.5-7 Mohs; Color: Reddish-brown, maroon, grey; Luster: Vitreous to waxy; Texture: Cryptocrystalline; Cleavage: None (conchoidal fracture); Specific Gravity: 2.6-2.7

Hardness: 6
Color: Reddish-brown, maroon, grey
Luster: Vitreous to waxy

Identified July 11, 2026More sedimentary →

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Physical properties

Hardness: 6.5-7 Mohs; Color: Reddish-brown, maroon, grey; Luster: Vitreous to waxy; Texture: Cryptocrystalline; Cleavage: None (conchoidal fracture); Specific Gravity: 2.6-2.7

Formation & geological history

Formed through the accumulation of silica-rich organic remains (like diatoms or radiolarians) or chemical precipitation from hydrothermal fluids in sedimentary environments. High iron oxide content gives it the red color.

Uses & applications

Historically used for stone tools (knapping) due to its sharp edges; currently used for decorative purposes, lapidary work (jewelry), and as a collector's specimen.

Geological facts

The reddish variety of chert is commonly known as Jasper. Because of its conchoidal fracture, it was a primary material for prehistoric arrowheads and scrapers.

Field identification & locations

Identify in the field by its hardness (scratches glass), waxy luster on fresh surfaces, and smooth, curved (conchoidal) fractures. Found in riverbeds and sedimentary formations worldwide.