sedimentary
Chert (or Jasper)
Cryptocrystalline Quartz (SiO2)
Hardness: 7 on Mohs scale; Color: Dark brown to black with reddish-brown oxidation; Luster: Waxy to dull; Fracture: Conchoidal (shell-like curves); Structure: Cryptocrystalline.
- Hardness
- 7 on Mohs scale
- Color
- Dark brown to black with reddish-brown oxidation
- Luster
- Waxy to dull
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Physical properties
Hardness: 7 on Mohs scale; Color: Dark brown to black with reddish-brown oxidation; Luster: Waxy to dull; Fracture: Conchoidal (shell-like curves); Structure: Cryptocrystalline.
Formation & geological history
Formed from the accumulation of microscopic silica-rich organic remains (like radiolarians or diatoms) or through chemical precipitation in marine environments; often found as nodules in limestone or as bedded deposits.
Uses & applications
Historically used for making stone tools (arrowheads, scrapers) due to its sharp edges when fractured; currently used in jewelry (as jasper), landscaping, and as an abrasive.
Geological facts
Chert has been used by humans for hundreds of thousands of years to create tools and start fires; the fracture properties allow for 'knapping' which creates edges sharper than a surgical scalpel.
Field identification & locations
Identify in the field by its waxy luster, extreme hardness (it will scratch glass), and distinctive curved, glass-like fracture surfaces; commonly found in river beds or eriding out of limestone cliffs.
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