sedimentary
Chert (White Chert/Flint)
Silicon Dioxide (SiO2)
Hardness: 7 (Mohs scale); Color: White to light grey; Luster: Dull to waxy; Crystal structure: Microcrystalline/Cryptocrystalline; Cleavage: None (conchoidal fracture); Specific gravity: 2.65
- Hardness
- 7 (Mohs scale)
- Color
- White to light grey
- Luster
- Dull to waxy
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Physical properties
Hardness: 7 (Mohs scale); Color: White to light grey; Luster: Dull to waxy; Crystal structure: Microcrystalline/Cryptocrystalline; Cleavage: None (conchoidal fracture); Specific gravity: 2.65
Formation & geological history
Formed through the accumulation of silica-rich organic remains (like radiolarians or diatoms) or by chemical precipitation in marine or groundwater environments. Found in Paleozoic to Cenozoic carbonate rock layers.
Uses & applications
Historically used for stone tools and weapons (arrowheads) due to sharp edges; currently used as a raw material for ceramics, construction aggregate, and by flint-knappers.
Geological facts
Chert is so hard it can scratch glass and steel. This specimen shows a weathered, rounded exterior often referred to as a 'patina' or cortex, common in river-worn or desert-exposed pieces.
Field identification & locations
Identify in the field by its hardness (cannot be scratched by a knife) and characteristic shell-like (conchoidal) fractures where it has been chipped. Commonly found in limestone beds or as nodules in riverbeds.
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