Chert (Field Stone/Jasper variety)

Physical Properties

Hardness: 6.5-7.0 (Mohs scale), Color: tan, grey, brown. Luster: waxy to dull, Crystal structure: Trigonal (microcrystalline), Cleavage: None (conchoidal fracture), Specific Gravity: 2.65.

Formation & Geological History

Formed through the accumulation of silica-rich microfossils (like radiolarians or diatoms) or by chemical precipitation in marine or groundwater environments. This specimen appears as a river-worn or glacial till cobble.

Uses & Applications

Historically used for stone tools (arrowheads/scrapers) due to sharp edges; currently used for road base, decorative landscaping, and occasionally lapidary work if highly colored.

Geological Facts

Chert was one of the most important minerals for early humans because its conchoidal fracture allows it to be shaped into razor-sharp cutting tools. It is chemically identical to flint and jasper.

Field Identification & Locations

Identify in the field by its waxy texture and shell-like (conchoidal) fracture when broken. It cannot be scratched by a steel knife. Common in limestone regions and gravel pits.

Identified on: 4/19/2026

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