sedimentary

Chert (Jasper/Chalcedony)

Microcrystalline Quartz (SiO2)

AI-generated identification · may be incorrect

Hardness: 6.5-7 (cannot be scratched by steel), Color: Tan to dark brown with banding, Luster: Waxy to vitreous, Structure: Cryptocrystalline, Fracture: Conchoidal

Hardness: 6

Identified May 5, 2026More sedimentary →

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Physical properties

Hardness: 6.5-7 (cannot be scratched by steel), Color: Tan to dark brown with banding, Luster: Waxy to vitreous, Structure: Cryptocrystalline, Fracture: Conchoidal

Formation & geological history

Formed via the accumulation of silica-rich microfossils (like radiolarians) on the ocean floor, or through the replacement of limestone by silica-rich fluids. Can be billions of years old.

Uses & applications

Historically used for stone tools (knapping) due to its sharp edges. Today used as a decorative river rock, for aquarium gravel, and occasionally as minor gemstone material.

Geological facts

Chert was the primary material for spear tips and arrowheads in prehistoric times because it breaks with a conchoidal fracture, creating razor-sharp edges.

Field identification & locations

Identified by its extreme hardness, waxy texture, and shell-like (conchoidal) fracture patterns. Frequently found as pebbles and cobbles in riverbeds or on beaches.