sedimentary
Chert (Flint)
Silicon Dioxide (SiO2)
Hardness: 7 (Mohs scale); Color: Brown, grey, tan; Luster: Waxy to dull; Crystal structure: Cryptocrystalline; Cleavage: None (conchoidal fracture); Specific gravity: 2.65
- Hardness
- 7 (Mohs scale)
- Color
- Brown, grey, tan
- Luster
- Waxy to dull
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Physical properties
Hardness: 7 (Mohs scale); Color: Brown, grey, tan; Luster: Waxy to dull; Crystal structure: Cryptocrystalline; Cleavage: None (conchoidal fracture); Specific gravity: 2.65
Formation & geological history
Formed as nodules or bedded deposits in sedimentary rocks, primarily through the accumulation of siliceous microfossils or chemical precipitation from silica-rich groundwater. Found in deposits ranging from Precambrian to Cenozoic eras.
Uses & applications
Historically used for stone tools and starting fires; currently used as construction aggregate, road surfacing, and decorative landscaping stone.
Geological facts
Chert is so hard it can scratch steel. It was the primary material used by prehistoric humans for creating arrowheads, scrapers, and knives due to its sharp, glass-like edges when fractured.
Field identification & locations
Identify in the field by its waxy texture and sharp, curved fracture surfaces. It is ubiquitous in limestone and chalk regions globally.
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