sedimentary
Chert (Iron-stained)
Silicon Dioxide (SiO2)
Hardness: 7 (Mohs scale), Color: Brown to tan with iron staining, Luster: Waxy to dull, Crystal structure: Microcrystalline/Cryptocrystalline, Cleavage: None (conchoidal fracture), Specific Gravity: 2.65
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Physical properties
Hardness: 7 (Mohs scale), Color: Brown to tan with iron staining, Luster: Waxy to dull, Crystal structure: Microcrystalline/Cryptocrystalline, Cleavage: None (conchoidal fracture), Specific Gravity: 2.65
Formation & geological history
Formed from the accumulation of siliceous remains of microscopic organisms (like diatoms or radiolarians) or through the chemical precipitation of silica in groundwater. This specimen shows significant iron oxide staining from exposure to mineral-rich fluids.
Uses & applications
Historically used for stone tools (arrowheads and scrapers) due to its sharp edges; currently used for road ballast, construction aggregate, and as a collector's specimen.
Geological facts
Chert is so hard it can scratch steel. It was one of the most important minerals for early humans because of its ability to fracture into extremely sharp, predictable edges.
Field identification & locations
Identify in the field by its conchoidal (shell-like) fracture, extreme hardness (cannot be scratched by a knife), and smooth, waxy texture. It is commonly found in limestone or dolomite formations.
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