sedimentary
Chert (Iron-stained)
Microcrystalline Quartz (SiO2)
Hardness: 7 (Mohs scale), Color: tan, grey, yellow-brown, rust-red, Luster: waxy to dull, Crystal Structure: Cryptocrystalline, Cleavage: None (conchoidal fracture), Specific Gravity: 2.65
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Physical properties
Hardness: 7 (Mohs scale), Color: tan, grey, yellow-brown, rust-red, Luster: waxy to dull, Crystal Structure: Cryptocrystalline, Cleavage: None (conchoidal fracture), Specific Gravity: 2.65
Formation & geological history
Formed through the accumulation of silica-rich organic remains (such as diatoms) or by chemical precipitation in saltwater and groundwater. Most specimens are from the Phanerozoic eon.
Uses & applications
Historically used for stone tools and flintknapping. Currently used for road gravel, construction aggregate, and occasionally tumbled for jewelry/decor.
Geological facts
Chert is so hard it can easily scratch glass and stainless steel. It was the primary material used by prehistoric humans for making arrowheads and scrapers due to its sharp conchoidal edges.
Field identification & locations
Identify by its extreme hardness, waxy texture, and shell-like (conchoidal) fracture pattern. Found globally in limestone formations and riverbeds.
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