sedimentary

Yellow Chert (Jasper)

Microcrystalline Quartz (SiO2)

Hardness: 6.5-7 on Mohs scale; Color: Opaque yellow to mustard brown; Luster: Waxy to vitreous; Crystal structure: Trigonal (microcrystalline); Cleavage: None (conchoidal fracture); Specific gravity: 2.6-2.7

Hardness: 6
Color: Opaque yellow to mustard brown
Luster: Waxy to vitreous

Identified March 20, 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 chemical precipitation in marine environments. The yellow color is typically caused by iron oxide inclusions (goethite). Age varies widely from Precambrian to Cenozoic.

Uses & applications

Used as lapidary material for jewelry (cabochons), ornamental carvings, and historically used for stone tools and arrowheads due to its sharp edges when fractured.

Geological facts

Chert is so durable that it often survives long after the surrounding rock has weathered away; it was one of the first minerals used by early humans for fire-starting and weaponry.

Field identification & locations

Identify in the field by its smooth, shell-like (conchoidal) fracture surfaces and the fact that it cannot be scratched by a steel knife. Common in riverbeds, glacial till, and embedded in limestone/dolomite formations.

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Chert Breccia

Brecciated Chert (Microcrystalline Silica)

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