Chert (Jasper variation)

Physical Properties

Hardness: 6.5–7 on Mohs scale. Color: Opaque brown, reddish-brown. Luster: Dull to waxy. Crystal structure: Trigonal (microcrystalline/cryptocrystalline). Cleavage: None (conchoidal fracture). Specific gravity: 2.6–2.7.

Formation & Geological History

Formed through the accumulation of silica-rich organic remains or chemical precipitation in sedimentary environments. Common in marine limestone beds and as nodules. Can date from the Precambrian to Cenozoic.

Uses & Applications

Historically used for stone tools (knapping) due to its sharp edges. Today used as an ornamental stone, in decorative landscaping, and for lapidary work/jewelry.

Geological Facts

Because of its high silica content and density, it was the primary material used by prehistoric humans to create arrowheads, scrapers, and knives. Jasper is the name specifically given to the more colorful, opaque varieties of chert.

Field Identification & Locations

Identify by its 'shell-like' conchoidal fracture patterns and inability to be scratched by a steel knife. Commonly found in riverbeds, glacial tills, and weathering out of limestone formations. Highly prized by flintknappers.

Identified on: 4/18/2026

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