sedimentary

Chert (Jasper/Flint variety)

Microcrystalline or Cryptocrystalline Quartz (SiO2)

Hardness: 7 (Mohs scale); Color: Variegated greens and tans due to mineral impurities; Luster: Waxy to sub-vitreous; Crystal Structure: Trigonal (microscopic); Cleavage: None (conchoidal fracture); Specific Gravity: 2.6-2.7

Hardness: 7 (Mohs scale)
Color: Variegated greens and tans due to mineral impurities
Luster: Waxy to sub-vitreous

Identified February 20, 2026More sedimentary →

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Physical properties

Formation & geological history

Formed through the accumulation of silica-rich organic remains (like diatoms or radiolaria) or chemical precipitation in marine environments. This specimen appears water-worn, suggesting transport in a river or stream bed.

Uses & applications

Historically used for stone tools (arrowheads, scrapers) due to conchoidal fracturing. Modern uses include abrasives, decorative stones, river rock for landscaping, and lapidary work.

Geological facts

Chert is so hard it can strike sparks against steel, a property utilized in flintlock firearms. Its toughness and predictability when knapped made it the primary 'technology' for humans for millions of years.

Field identification & locations

Identify by its extreme hardness (cannot be scratched by a steel knife) and its smooth, shell-like (conchoidal) fracture surfaces. Commonly found in gravel pits, riverbeds, and limestone outcrops.

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