sedimentary
Chert (Flint/Nodule)
Silicon Dioxide (SiO2)
Hardness: 7 on Mohs scale. Color: Tan, brown, gray, to yellowish-brown with a dull weathering rind. Luster: Dull to waxy. Microcrystalline texture with shell-like conchoidal fracture under the weathered exterior.
- Hardness
- 7 on Mohs scale
- Luster
- Dull to waxy
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Physical properties
Hardness: 7 on Mohs scale. Color: Tan, brown, gray, to yellowish-brown with a dull weathering rind. Luster: Dull to waxy. Microcrystalline texture with shell-like conchoidal fracture under the weathered exterior.
Formation & geological history
Formed through the accumulation of siliceous oozes or replacement of carbonate rocks (such as limestone or chalk) by silica dissolved in groundwater. Commonly found in marine sedimentary basins.
Uses & applications
Historically used for stone tools, arrowheads, and striking fire. Today used primarily as road aggregate, construction material, and decorative landscape rock.
Geological facts
Chert nodules often feature a chalky white or tan weathered exterior crust called a rind, hiding a much denser, glassy microcrystalline quartz core inside.
Field identification & locations
Look for rounded or irregular nodules embedded in or weathered out from limestone beds. Hardness 7 prevents scratch by steel.
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