sedimentary

Chert (Jasper-rich River Cobble)

Cryptocrystalline Quartz (SiO2)

AI-generated identification · may be incorrect

Hardness: 6.5-7 on Mohs scale. Color: Brownish-red to orange due to iron oxide (limonite/hematite). Luster: Dull to waxy. Structure: Microcrystalline with no visible grains. Cleavage: None (conchoidal fracture).

Hardness: 6
Color: Brownish-red to orange due to iron oxide (limonite/hematite)
Luster: Dull to waxy

Identified June 25, 2026More sedimentary →

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Physical properties

Formation & geological history

Formed through the chemical precipitation of silica or the replacement of limestone by silica-rich fluids. This specific specimen is a water-worn river cobble, rounded by mechanical weathering in a high-energy fluvial environment.

Uses & applications

Abrasives, decorative landscaping, historical tool-making (flintknapping), and basic jewelry cabochons.

Geological facts

Chert is so durable that it can survive millions of years of river transport. It was the primary material used by prehistoric humans for creating sharp-edged tools like arrowheads and scrapers.

Field identification & locations

Identify by its hardness (it will scratch glass), smooth waxy texture when wet, and curved 'conchoidal' fractures on broken edges. Common in riverbeds and limestone regions.