sedimentary
Chert (River Siltstone/Quartzite)
Sedimentary Cryptocrystalline Quartz (SiO2)
Hardness: 7 (Mohs scale), Color: tan to light brown, Luster: dull to waxy, Crystal Structure: Microcrystalline, Cleavage: None (conchoidal fracture), Specific Gravity: 2.65
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Physical properties
Hardness: 7 (Mohs scale), Color: tan to light brown, Luster: dull to waxy, Crystal Structure: Microcrystalline, Cleavage: None (conchoidal fracture), Specific Gravity: 2.65
Formation & geological history
Formed from the accumulation of silica-rich organic remains or chemical precipitation in ancient marine or groundwater environments. This specimen appears water-worn, likely sourced from a riverbed or glacial deposit.
Uses & applications
Historically used for stone tools (flintknapping); currently used as construction aggregate, road base, and occasionally as decorative landscaping stone.
Geological facts
Chert is so hard it can scratch steel. It often originates from the silica skeletons of prehistoric marine organisms like diatoms and radiolarians.
Field identification & locations
Identify by its extreme hardness and smooth, curved (conchoidal) fractures when broken. It is extremely common in river gravels and sedimentary basins worldwide.
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