sedimentary
Chert (Jasper/Flint)
Silicon Dioxide (SiO2)
Hardness: 7 (Mohs scale); Color: Brown, tan, ochre; Luster: Dull to waxy; Structure: Microcrystalline; Cleavage: None (conchoidal fracture); Specific Gravity: 2.65
- Hardness
- 7 (Mohs scale)
- Color
- Brown, tan, ochre
- Luster
- Dull to waxy
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Physical properties
Hardness: 7 (Mohs scale); Color: Brown, tan, ochre; Luster: Dull to waxy; Structure: Microcrystalline; Cleavage: None (conchoidal fracture); Specific Gravity: 2.65
Formation & geological history
Formed through the accumulation of silica-rich organic remains or chemical precipitation in marine environments, often replacing limestone or chalk. Can range from Precambrian to Cenozoic age.
Uses & applications
Historical use for stone tools (knapping), construction aggregate, and occasionally used as a gemstone (Jasper) when colorful.
Geological facts
Chert has a distinctive conchoidal (shell-like) fracture which creates sharp edges; this made it the primary material for prehistoric arrowheads and scrapers.
Field identification & locations
Identify by its 'ring' when struck, its ability to scratch glass, and its smooth, curved break surfaces. Commonly found in nodules within limestone or as river-worn cobbles.
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