sedimentary
Chert (Flint Nodules)
Microcrystalline Quartz (SiO2)
Hardness: 7 (Mohs scale), Color: tan, brownish-yellow with iron staining, Luster: waxy to dull, Crystal structure: microcrystalline, Cleavage: none (conchoidal fracture)
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Physical properties
Hardness: 7 (Mohs scale), Color: tan, brownish-yellow with iron staining, Luster: waxy to dull, Crystal structure: microcrystalline, Cleavage: none (conchoidal fracture)
Formation & geological history
Formed in marine environments during diagenesis as silica-rich fluids replace carbonate material or precipitate in voids. This specimen shows river-worn rounding and pocketed dissolution.
Uses & applications
Historically used for making stone tools; currently used as road aggregate, in landscaping, and as a common find for mineral hobbyists.
Geological facts
Chert is so hard it can strike sparks against steel. It was the primary material for spearheads and arrowheads for thousands of years due to its razor-sharp conchoidal fracture.
Field identification & locations
Identified by its extreme hardness (cannot be scratched by a steel knife) and its smooth, waxy feel in areas not covered by weathering. Commonly found in riverbeds and limestone outcrops.
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