sedimentary
Chert Pebble (River Siltstone / Jasper)
Microcrystalline Quartz (SiO2)
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
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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.
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