sedimentary
Chert (Flint)
Microcrystalline Quartz (SiO2)
Hardness: 7 Mohs scale; Color: Cream to white with brown weathering; Luster: Waxy to dull; Crystal structure: Cryptocrystalline; Cleavage: None, exhibits conchoidal fracture
- Hardness
- 7 Mohs scale
- Color
- Cream to white with brown weathering
- Luster
- Waxy to dull
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Physical properties
Hardness: 7 Mohs scale; Color: Cream to white with brown weathering; Luster: Waxy to dull; Crystal structure: Cryptocrystalline; Cleavage: None, exhibits conchoidal fracture
Formation & geological history
Biogenic or chemical precipitation of silica in marine environments, often replacing carbonate material; can date from Precambrian to Cenozoic eras.
Uses & applications
Historically used for making stone tools (arrowheads); currently used in road construction, landscaping, and occasionally as decorative gravel or for fire-starting kits.
Geological facts
Because it fractures conchoidally into very sharp edges, chert was the primary material for survival technology for thousands of years. It occurs as nodules or layers in limestone.
Field identification & locations
Identify by its hardness (cannot be scratched by steel), waxy texture, and the way it breaks into smooth curves. Often found in riverbeds or limestone outcroppings.
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