sedimentary
Chert (Nodular Chert)
Silicon Dioxide (SiO2)
Hardness: 7 (Mohs scale), Color: tan, grey, brown with waxy luster, Crystal structure: microcrystalline/cryptocrystalline, Cleavage: none (conchoidal fracture), Specific gravity: 2.5-2.8
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Physical properties
Hardness: 7 (Mohs scale), Color: tan, grey, brown with waxy luster, Crystal structure: microcrystalline/cryptocrystalline, Cleavage: none (conchoidal fracture), Specific gravity: 2.5-2.8
Formation & geological history
Formed through the accumulation of silica-rich organic remains (like radiolaria or diatoms) or chemical precipitation in marine environments; often found as nodules in limestone or chalk beds.
Uses & applications
Historically used for stone tools/weapons; currently used for road surfacing, as grinding media in ball mills, and occasionally as an ornamental landscape stone.
Geological facts
Chert was one of the most important minerals for early humans because its conchoidal fracture produces razor-sharp edges used for arrows and knives. It is also often associated with flint.
Field identification & locations
Identify by its extreme hardness (cannot be scratched by a steel knife) and its smooth, shell-like (conchoidal) breaking surface. Look for it within limestone outcrops.
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Cone-in-cone structure (Limestone)
Cone-in-cone structure (Secondary Sedimentary Structure)
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Chert Breccia
Brecciated Chert (Microcrystalline Silica)
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Sandstone Grain
Clastic Sedimentary Rock Grain (SiO2 dominated)
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Shale or Slaty Mudstone
Argillaceous sedimentary rock
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Sandstone
Arenite (primarily SiO2)
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