sedimentary
Chert (Jasper)
Silicon Dioxide (SiO2)
Hardness: 6.5-7 on Mohs scale; Color: Reddish-brown to tan; Luster: Dull to waxy; Crystal Structure: Microcrystalline/Cryptocrystalline; Cleavage: None (conchoidal fracture); Specific Gravity: 2.6-2.7
- Hardness
- 6
- Color
- Reddish-brown to tan
- Luster
- Dull to waxy
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Physical properties
Hardness: 6.5-7 on Mohs scale; Color: Reddish-brown to tan; Luster: Dull to waxy; Crystal Structure: Microcrystalline/Cryptocrystalline; Cleavage: None (conchoidal fracture); Specific Gravity: 2.6-2.7
Formation & geological history
Formed from the accumulation of silica-rich micro-organisms on the ocean floor or through the chemical precipitation of silica-rich fluids in sedimentary rock voids.
Uses & applications
Historically used for making stone tools (arrowheads/scrapers) due to its sharp edges; currently used for lapidary work, jewelry, and as aquarium or landscaping gravel.
Geological facts
This specimen shows the characteristic conchoidal (shell-like) fracture pattern common to silica rocks. Chert is incredibly durable and can survive millions of years of erosion.
Field identification & locations
Identifiable by its hardness (it will scratch glass) and waxy luster when freshly broken. Found globally in limestone and chalk beds or as river cobbles. Look for smooth, curved break patterns.
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