sedimentary
Chert (Limestone-based)
Silicon Dioxide (SiO2) within Carbonate host
Hardness: 7 (Mohs scale), Color: light grey to tan/white, Luster: dull to waxy, Crystal Structure: Microcrystalline (Cryptocrystalline), Cleavage: None (Conchoidal fracture), Specific Gravity: 2.65
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Physical properties
Hardness: 7 (Mohs scale), Color: light grey to tan/white, Luster: dull to waxy, Crystal Structure: Microcrystalline (Cryptocrystalline), Cleavage: None (Conchoidal fracture), Specific Gravity: 2.65
Formation & geological history
Formed through the chemical precipitation of silica-rich fluids within prehistoric marine limestone or chalk beds. Most specimens date back to the Paleozoic or Mesozoic eras.
Uses & applications
Historically used for stone tools/arrowheads. Modern uses include road aggregate, decorative landscaping, and occasionally as a source of silica for glassmaking.
Geological facts
Chert is so hard it can scratch steel and was used by ancient civilizations to create fire by striking it against iron pyrite or steel to produce sparks.
Field identification & locations
Identify by its hardness (cannot be scratched by a knife) and smooth, shell-like (conchoidal) fractures. Common in riverbeds and limestone outcrops globally.
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Cone-in-cone structure (Secondary Sedimentary Structure)
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Chert Breccia
Brecciated Chert (Microcrystalline Silica)
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Clastic Sedimentary Rock Grain (SiO2 dominated)
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