sedimentary
Chert (Nodule)
Silicon Dioxide (SiO2)
Hardness: 7 (Mohs), Color: Brownish-tan with dark inclusions, Luster: Dull to waxy, Structure: Microcrystalline/Cryptocrystalline, Fracture: Conchoidal, Specific Gravity: 2.6
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Physical properties
Hardness: 7 (Mohs), Color: Brownish-tan with dark inclusions, Luster: Dull to waxy, Structure: Microcrystalline/Cryptocrystalline, Fracture: Conchoidal, Specific Gravity: 2.6
Formation & geological history
Formed through the accumulation of silica-rich microfossils or precipitation from silica-rich groundwater within limestone or chalk beds. Commonly found in Mesozoic or Paleozoic sedimentary layers.
Uses & applications
Historically used for stone tools (flintknapping); currently used in road construction, as an abrasive, and by collectors as display specimens.
Geological facts
Chert is a cryptocrystalline variety of quartz. When struck against steel, it can produce sparks, which led to its historical use in flintlock firearms.
Field identification & locations
Identified by its extreme hardness (cannot be scratched by steel), waxy texture on fresh surfaces, and smooth, curved conchoidal fractures. Commonly found in riverbeds and limestone outcrops.
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