sedimentary
Chert (specifically Jasper or Flint variant)
Cryptocrystalline Quartz (SiO2)
Hardness: 6.5-7 on Mohs scale; Color: Brown, tan, reddish-yellow; Luster: Dull to waxy; Structure: Microcrystalline; Cleavage: None (conchoidal fracture); Specific Gravity: 2.6-2.7
- Hardness
- 6
- Color
- Brown, tan, reddish-yellow
- Luster
- Dull to waxy
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Physical properties
Hardness: 6.5-7 on Mohs scale; Color: Brown, tan, reddish-yellow; Luster: Dull to waxy; Structure: Microcrystalline; Cleavage: None (conchoidal fracture); Specific Gravity: 2.6-2.7
Formation & geological history
Formed as nodules or beds in limestone or chalk through the accumulation of silica-rich microfossils or chemical precipitation from groundwater. It can range in age from Precambrian to Cenozoic.
Uses & applications
Historically used for stone tools/arrowheads due to sharp edges; currently used for landscaping, road aggregate, and sometimes as a minor gemstone for lapidary work.
Geological facts
Chert was one of the most important minerals to prehistoric humans because its conchoidal fracture allows it to be shaped into razor-sharp blades and points.
Field identification & locations
Identify by its 'shell-like' conchoidal fracture patterns and inability to be scratched by a steel knife. Frequently found in riverbeds, gravel pits, and desert pavement.
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