sedimentary

Chert (Jasper variety)

Silicon Dioxide (SiO2)

Hardness: 6.5-7 on Mohs scale. Color: Brown, reddish-brown, and tan banding. Luster: Waxy to dull. Crystal Structure: Microcrystalline/Cryptocrystalline (Hexagonal). Cleavage: None, exhibits conchoidal (shell-like) fracture. Specific Gravity: 2.6-2.7.

Hardness: 6
Color: Brown, reddish-brown, and tan banding
Luster: Waxy to dull

Identified June 30, 2026More sedimentary →

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Physical properties

Formation & geological history

Formed through the accumulation of silica-rich organic remains (like diatoms or radiolarians) or through the precipitation of silica in groundwater within sedimentary host rocks. Common in geological formations ranging from the Precambrian to the present.

Uses & applications

Historically used for stone tools (arrowheads/scrapers) due to sharp edges. Today used in jewelry (cabochons), as decorative stones, and in lapidary arts.

Geological facts

Chert is so durable that it often survives long after its surrounding host rock has eroded away. The reddish-brown variety is often referred to as Jasper, colored by iron oxide inclusions.

Field identification & locations

Identify in the field by its hardness (it will scratch glass), waxy feel, and curved, glass-like fracture surfaces. Often found in riverbeds or as nodules within limestone or chalk layers.