sedimentary

Chert Pebble (River Siltstone / Jasper)

Microcrystalline Quartz (SiO2)

AI-generated identification · may be incorrect

Hardness: 6.5-7 on Mohs scale; Color: Brownish-tan to dark grey; Luster: Waxy to dull, shiny when wet; Fracture: Conchoidal; Specific Gravity: 2.65

Hardness: 6
Color: Brownish-tan to dark grey
Luster: Waxy to dull, shiny when wet

Identified July 28, 2026More sedimentary →

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Physical properties

Hardness: 6.5-7 on Mohs scale; Color: Brownish-tan to dark grey; Luster: Waxy to dull, shiny when wet; Fracture: Conchoidal; Specific Gravity: 2.65

Formation & geological history

Formed by the precipitation of silica-rich fluids or accumulation of siliceous organism remains (such as radiolarians or diatoms) on oceanic/lake beds, followed by diagenesis and fluvial weathering.

Uses & applications

Used historically for stone tools and flintknapping; modern uses include road aggregate, landscape gravel, decorative river stones, and rock tumbling.

Geological facts

Chert is extremely durable and chemically inert. Because of its hardness and conchoidal fracture pattern, ancient humans widely used varieties of chert like flint to make arrowheads and cutting tools.

Field identification & locations

Look for rounded, smooth pebbles in riverbeds or gravel deposits that cannot be easily scratched by steel. It breaks with sharp, curved conchoidal edges.