sedimentary

Chert (Jasper variation)

Microcrystalline Quartz (SiO2)

Hardness: 6.5-7 on Mohs scale. Color: Opaque brown, tan, and yellow-orange due to iron oxides. Luster: Waxy to dull. Crystal structure: Cryptocrystalline. Cleavage: None (conchoidal fracture). Specific gravity: 2.6-2.7.

Hardness: 6
Color: Opaque brown, tan, and yellow-orange due to iron oxides
Luster: Waxy to dull

Identified April 12, 2026More sedimentary →

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Physical properties

Formation & geological history

Formed from the accumulation of silica-rich marine organisms (like diatoms or radiolaria) or by chemical precipitation in groundwater that replaces organic material or limestone. Can range from Precambrian to Cenozoic in age.

Uses & applications

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

Geological facts

Chert is so durable that it often survives as 'river rocks' long after the surrounding bedrock has eroded away. Native Americans used this specific material for arrowheads and scrapers because it breaks into razor-sharp edges.

Field identification & locations

Identify in the field by its waxy luster, smoothness, and conchoidal (shell-like) fracture patterns. It cannot be scratched by a steel knife. Common in stream beds and limestone outcrops.

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Chert Breccia

Brecciated Chert (Microcrystalline Silica)

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